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

[Tom Stellard via llvm-commits]

tstellar wrote:

> > > > I might be missing something,
> > > 
> > > 
> > > `MCRegister RegNo = MatchRegisterName(Name);`
> > > With a brief look at the generated code it seems to me that it matches only lower case names.
> > 
> > 
> > Yes, I think that's the issue.
> 
> That behaviour have not changed AFAIK.

The behavior of the generated function has not changed, but that function is now being used to parse register names where it wasn't before.

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