target/riscv: rvv-1.0: remove amo operations instructions

target/riscv: rvv-1.0: remove amo operations instructions

Vector AMOs are removed from standard vector extensions. Will be added
later as separate Zvamo extension, but will need a different encoding
from earlier proposal.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-19-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>