target/riscv: update cur_pmbase/pmmask based on mode affected by MPRV

Pointer mask is also affected by MPRV which means cur_pmbase/pmmask
should also take MPRV into consideration. As pointer mask for instruction
is not supported currently, so we can directly update cur_pmbase/pmmask
based on address related mode and xlen affected by MPRV now.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-Id: <20230614032547.35895-3-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>