cmd/internal/obj/riscv: add encoding for compressed riscv64 instructions

cmd/internal/obj/riscv: add encoding for compressed riscv64 instructions

Regenerate instruction encodings for riscv64, including rv64_c, rv_c
and rv_c_d.

Updates #71105

Change-Id: I004cc00290bf018ebb848592d84d924481f03851
Reviewed-on: https://go-review.googlesource.com/c/go/+/523476
Reviewed-by: Meng Zhuo <mengzhuo1203@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>