target/riscv: Separate pmp_update_rule() in pmpcfg_csr_write

target/riscv: Separate pmp_update_rule() in pmpcfg_csr_write

Use pmp_update_rule_addr() and pmp_update_rule_nums() separately to
update rule nums only once for each pmpcfg_csr_write. Then remove
pmp_update_rule() since it become unused.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230517091519.34439-12-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>