cmd/compile/internal: add ABI register information for riscv64
cmd/compile/internal: add ABI register information for riscv64

This CL adds the defines for ABI registers on riscv64.

Updates #40724

Change-Id: I53a89d88b6feb1a88cf7008b8484d444791e8a55
Reviewed-on: https://go-review.googlesource.com/c/go/+/356519
Trust: mzh <3e6d300a356a3b86bc195677414a9ec5508ca893@golangcn.org>
Run-TryBot: mzh <3e6d300a356a3b86bc195677414a9ec5508ca893@golangcn.org>
Reviewed-by: Joel Sing <4816dabf8db1bc6cac35b3a24cab2ff844b5b0c7@sing.id.au>
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,CAFxX/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,golang/go,nawawi/go,nawawi/go,golang/go,golang/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,CAFxX/go,CAFxX/go