target/riscv: Move pmp_get_tlb_size apart from get_physical_address_pmp

target/riscv: Move pmp_get_tlb_size apart from get_physical_address_pmp

pmp_get_tlb_size can be separated from get_physical_address_pmp and is only
needed when ret == TRANSLATE_SUCCESS.

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230517091519.34439-3-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>