lib: utils: Allow PLIC functions to be used for multiple PLICs

We extend all PLIC functions to have a "struct plic_data *"
parameter pointing to PLIC details. This allows platforms to
use these functions for multiple PLIC instances.

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