[llvm] [RISCV][GISel] Add FP calling convention support (PR #69138)

[Brandon Wu via llvm-commits]

4vtomat wrote:

> > Do we also want to add test cases for using `float` as incoming/outgoing type? since it uses different register classes other than `$x1-$x31`.
> 
> Like `callee_float_in_fpr` in `calling-conv-ilp32f-ilp32d-common.ll`?

Oh I missed the file since it's folded lol~
I see, yes it's what I'm talking about.

https://github.com/llvm/llvm-project/pull/69138