[llvm] [RISCV,GISel] Add legalizer for G_ABS (PR #67577)

[via llvm-commits]

tschuett wrote:

Nit. The IRTranslator has probably generated something like:
```
G_INTRINSIC intrinsic(@llvm.abs.v2.32)
```
llvm.abs* is automatically supported. You code does not contain intrinsics.

https://github.com/llvm/llvm-project/pull/67577