lib: sbi: Detect PMP granularity and number of address bits

As per RISC-V privilege specification, a platform may choose to implement
a coarser granularity scheme for PMP addresses. In that case, we shouldn't
allow any pmp region size smaller than the platform supports. A platform
may not also implement all the bits for a PMP address specified in the priv
specification.

The pmp range granularity and address bits should be detected dynamically
before detecing PMP regions. Any pmp modification request beyond these detected
value must not succeed.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>