cmd/internal/obj/riscv: add check for invalid shift amount input

cmd/internal/obj/riscv: add check for invalid shift amount input

Current RISCV64 assembler do not check the invalid shift amount. This CL
adds the check to avoid generating invalid instructions.

Fixes #57755

Change-Id: If33877605e161baefd98c50db1f71641ca057507
Reviewed-on: https://go-review.googlesource.com/c/go/+/461755
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>