target/riscv: Replace DisasContext.w with DisasContext.ol

target/riscv: Replace DisasContext.w with DisasContext.ol

In preparation for RV128, consider more than just "w" for
operand size modification.  This will be used for the "d"
insns from RV128 as well.

Rename oper_len to get_olen to better match get_xlen.

Reviewed-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20211020031709.359469-10-richard.henderson@linaro.org
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>