[llvm] [MIPS] Add Scheduling model for MIPS i6400 and i6500 CPUs (PR #132704)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-nvptx-nvidia-win` running on `as-builder-8` while building `llvm` at step 7 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/54/builds/8671

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

```
Step 7 (test-build-unified-tree-check-llvm) failure: test (failure)
******************** TEST 'LLVM :: tools/llvm-mca/Mips/i6400.s' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 2
c:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\build\bin\llvm-mca.exe -mtriple=mips64el -mcpu=i6400 --mattr=msa -iterations=1 < C:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\llvm-project\llvm\test\tools\llvm-mca\Mips\i6400.s | c:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\build\bin\filecheck.exe C:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\llvm-project\llvm\test\tools\llvm-mca\Mips\i6400.s
# executed command: 'c:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\build\bin\llvm-mca.exe' -mtriple=mips64el -mcpu=i6400 --mattr=msa -iterations=1
# .---command stderr------------
# | c:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\build\bin\llvm-mca.exe: unable to get target for 'mips64el', see --version and --triple.
# `-----------------------------
# error: command failed with exit status: 1
# executed command: 'c:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\build\bin\filecheck.exe' 'C:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\llvm-project\llvm\test\tools\llvm-mca\Mips\i6400.s'
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  c:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\build\bin\filecheck.exe C:\buildbot\as-builder-8\llvm-nvptx-nvidia-win\llvm-project\llvm\test\tools\llvm-mca\Mips\i6400.s
# `-----------------------------
# error: command failed with exit status: 2

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/132704