[llvm] [NFC][PowerPC] Use tablegen's MatchRegisterName() (PR #111553)

[Tom Stellard via llvm-commits]

tstellar wrote:

I think this commit caused a regression in the dotnet9.0 build for Fedora:

```
             Consolidate compiler generated dependencies of target utilcodestaticnohost
             make[3]: Leaving directory '/builddir/build/BUILD/dotnet9.0-9.0.102-build/dotnet-9.0.1/src/runtime/artifacts/obj/coreclr/linux.ppc64le.Release'
             make  -f utilcode/CMakeFiles/utilcodestaticnohost.dir/build.make utilcode/CMakeFiles/utilcodestaticnohost.dir/build
             /builddir/build/BUILD/dotnet9.0-9.0.102-build/dotnet-9.0.1/src/runtime/src/coreclr/pal/src/arch/ppc64le/context2.S:140:15: error: invalid register name
              ld %r0, 0 +8(%R3)
```

https://github.com/llvm/llvm-project/pull/111553