target/riscv: Remove shift-one instructions (proposed Zbo in pre-0.93 draft-B)

target/riscv: Remove shift-one instructions (proposed Zbo in pre-0.93 draft-B)

The Zb[abcs] ratification package does not include the proposed
shift-one instructions. There currently is no clear plan to whether
these (or variants of them) will be ratified as Zbo (or a different
extension) or what the timeframe for such a decision could be.

Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Acked-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: 20210911140016.834071-8-philipp.tomsich@vrull.eu
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>