[llvm] [AMDGPU][AsmParser] Support true16 register suffix for valid register range (PR #143997)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Fixes SWDEV-537816.

Just to explain for people who do not have access to this, the use case is writing (or generating) assembler sources that want to use assembler expressions for VGPR numbers like:
```
v_cvt_f16_f32 v[N+1].h, v0
```

https://github.com/llvm/llvm-project/pull/143997