target/riscv: Alloc tcg global for cur_pm[mask|base]

target/riscv: Alloc tcg global for cur_pm[mask|base]

Replace the array of pm_mask/pm_base with scalar variables.
Remove the cached array value in DisasContext.

Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20220120122050.41546-13-zhiwei_liu@c-sky.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>