target/riscv: Add PMP state description

target/riscv: Add PMP state description

In the case of supporting PMP feature, add PMP state description
to vmstate_riscv_cpu.

'vmstate_pmp_addr' and 'num_rules' could be regenerated by
pmp_update_rule(). But there exists the problem of updating
num_rules repeatedly in pmp_update_rule(). So here extracts
pmp_update_rule_addr() and pmp_update_rule_nums() to update
'vmstate_pmp_addr' and 'num_rules' respectively.

Signed-off-by: Yifei Jiang <[email protected]>
Signed-off-by: Yipeng Yin <[email protected]>
Reviewed-by: Alistair Francis <[email protected]>
Message-id: 20201026115530[email protected]
Signed-off-by: Alistair Francis <[email protected]>