[llvm] [Mips] Support llvm.readcyclecounter intrinsic (PR #127553)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-expensive-checks-debian` running on `gribozavr4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/16/builds/13921

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/Mips/readcyclecounter.ll' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 1: /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc -mtriple=mipsel-linux-gnu -mcpu=mips32r2 < /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/CodeGen/Mips/readcyclecounter.ll | /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/CodeGen/Mips/readcyclecounter.ll --check-prefix=MIPSEL
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/FileCheck /b/1/llvm-clang-x86_64-expensive-checks-debian/llvm-project/llvm/test/CodeGen/Mips/readcyclecounter.ll --check-prefix=MIPSEL
+ /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc -mtriple=mipsel-linux-gnu -mcpu=mips32r2

# After Instruction Selection
# Machine code for function test_readcyclecounter: IsSSA, TracksLiveness

bb.0.entry:
  %0:gpr32 = RDHWR $hwr2, 0
  %1:gpr32 = ADDiu $zero, 0
  $v0 = COPY %0:gpr32
  $v1 = COPY %1:gpr32
  RetRA implicit $v0, implicit $v1

# End machine code for function test_readcyclecounter.

*** Bad machine code: Using an undefined physical register ***
- function:    test_readcyclecounter
- basic block: %bb.0 entry (0xad97ee0)
- instruction: %0:gpr32 = RDHWR $hwr2, 0
- operand 1:   $hwr2
LLVM ERROR: Found 1 machine code errors.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: /b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc -mtriple=mipsel-linux-gnu -mcpu=mips32r2
1.	Running pass 'Function Pass Manager' on module '<stdin>'.
2.	Running pass 'Verify generated machine code' on function '@test_readcyclecounter'
 #0 0x0000000003873c17 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x3873c17)
 #1 0x00000000038716ce llvm::sys::RunSignalHandlers() (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x38716ce)
 #2 0x00000000038742ca SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x00007fdd0d1f3140 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x13140)
 #4 0x00007fdd0cd07d51 raise (/lib/x86_64-linux-gnu/libc.so.6+0x38d51)
 #5 0x00007fdd0ccf1537 abort (/lib/x86_64-linux-gnu/libc.so.6+0x22537)
 #6 0x00000000037e3f2a llvm::report_fatal_error(llvm::Twine const&, bool) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x37e3f2a)
 #7 0x0000000002a60d6d (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2a60d6d)
 #8 0x0000000002a61ddb (anonymous namespace)::MachineVerifierLegacyPass::runOnMachineFunction(llvm::MachineFunction&) MachineVerifier.cpp:0:0
 #9 0x000000000295e083 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x295e083)
#10 0x0000000002eb3073 llvm::FPPassManager::runOnFunction(llvm::Function&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2eb3073)
#11 0x0000000002eb9aa1 llvm::FPPassManager::runOnModule(llvm::Module&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2eb9aa1)
#12 0x0000000002eb377d llvm::legacy::PassManagerImpl::run(llvm::Module&) (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x2eb377d)
#13 0x00000000008a3afc compileModule(char**, llvm::LLVMContext&) llc.cpp:0:0
#14 0x00000000008a0ecd main (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x8a0ecd)
#15 0x00007fdd0ccf2d7a __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x23d7a)
#16 0x000000000089fd1a _start (/b/1/llvm-clang-x86_64-expensive-checks-debian/build/bin/llc+0x89fd1a)
FileCheck error: '<stdin>' is empty.
...

```

</details>

https://github.com/llvm/llvm-project/pull/127553