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 <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>
Message-id: 20220120122050[email protected]
Signed-off-by: Alistair Francis <[email protected]>