cmd/internal/obj/riscv: add support for vector permutation instructions
Add support for vector permutation instructions to the RISC-V assembler.
This includes integer scalar move, floating point scalar move, slide up
and slide down, register gather, compression and whole vector register
move instructions.
Change-Id: I1da9f393091504fd81714006355725b8b9ecadea
Reviewed-on: https://go-review.googlesource.com/c/go/+/646780
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Carlos Amedee <carlos@golang.org> Reviewed-by: Mark Ryan <markdryan@rivosinc.com> Reviewed-by: Junyang Shao <shaojunyang@google.com> Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>