Rotates have been fixed up to only allow for reasonable rotate amounts
(ie, no rotates >7 on an 8b value etc.)  This fixes a problem with riscv
vector rotate instructions.

Signed-off-by: Dickon Hood <dickon.hood@codethink.co.uk>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230428144757.57530-9-lawrence.hunter@codethink.co.uk>
[rth: Mask shifts in both directions.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>