[llvm] [RISCV] Refactor X60 scheduling model helper classes. NFC. (PR #151572)

[Fangrui Song via llvm-commits]

MaskRay wrote:

This caused a ubsan failure https://lab.llvm.org/buildbot/#/builders/25/builds/10339/steps/9/logs/stdio 
```
FAILED: include/llvm/TargetParser/RISCVTargetParserDef.inc /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/include/llvm/TargetParser/RISCVTargetParserDef.inc 
cd /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/include/llvm/TargetParser && /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/bin/llvm-min-tblgen -gen-riscv-target-def -I/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include/llvm/TargetParser -I/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Target/RISCV -I/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/include -I/home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Target/RISCV/RISCV.td --write-if-changed -o RISCVTargetParserDef.inc -d RISCVTargetParserDef.inc.d && /usr/bin/cmake -E cmake_transform_depfile Ninja gccdepfile /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/include/llvm/TargetParser /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/include/llvm/TargetParser /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/include/llvm/TargetParser/RISCVTargetParserDef.inc.d /home/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/CMakeFiles/d/c37d9d265d35dce7a3ed35005d2e2dca9001ff421c599c9e4d4aa0b5a3458e83.d
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
```

https://github.com/llvm/llvm-project/pull/151572