target/riscv: rvv-1.0: integer scalar move instructions

target/riscv: rvv-1.0: integer scalar move instructions

* Remove "vmv.s.x: dothing if rs1 == 0" constraint.
* Add vmv.x.s instruction.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-37-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>