target/riscv: rvv-1.0: Add Zve64f support for vmulh variant insns

target/riscv: rvv-1.0: Add Zve64f support for vmulh variant insns

All Zve* extensions support all vector integer instructions,
except that the vmulh integer multiply variants that return the
high word of the product (vmulh.vv, vmulh.vx, vmulhu.vv, vmulhu.vx,
vmulhsu.vv, vmulhsu.vx) are not included for EEW=64 in Zve64*.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20220118014522.13613-5-frank.chang@sifive.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>