lib: sbi: Populate M-only Smepmp entries before setting mseccfg.MML

Based on sections 4.c and 4.d in Ch.2 of the Smepmp spec the PMP entries
must be programmed as below:
1. Program M-only entries
2. Enable mseccfg.MML
3. Program shared-region entries
4. Program SU-only entries

Co-developed-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>