[RISCV] Backport patch D153721
Created by: melonedo
This commit minimally adapts and backports change from https://reviews.llvm.org/D153721:
- The format of cv.avgu/srl/sra/sll/or/xor/and is changed;
- The extension name changed to
Xcvsimd
; - Old test files are replaced with
XCVsimd{-invalid}.s
Note that cv.srl/sra/sll still has an issue openhwgroup/corev-binutils-gdb#104