[llvm] [X86] Support EGPR (R16-R31) for APX (PR #67702)

[Shengchen Kan via llvm-commits]

KanRobert wrote:

> ```
> $ clang test.c -S -o - -m32
> ...
> test.c:2:7: error: register %r27 is only available in 64-bit mode
>     2 |   asm("addq %r27, %r29");
>       |       ^
> ```
> 
> But there is no error that `egpr` is not enabled
> 
> Also I've tried to use `m[no-]egpr`. Is it intended to not support it yet? UPD: the latter is clang's part, I guess it will be fixed in next patches.

The assembler/disassembler and clang support will be supported in following patches. I try not to make a patch too big。

https://github.com/llvm/llvm-project/pull/67702