lib: sbi: Change the order of PMP initialization

Configure PMP at last when all other initializations have been done.
Because if SMEPMP is detected, M-mode access to the S/U space will be
rescinded.

Signed-off-by: Himanshu Chauhan <hchauhan@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>