gic_500: Make redistributor init code smp aware

- Use array for storing per-core mapping of the redistributor register
mappings.
- Locate the base address of each of these mappings based on iterating
through the full device mappings looking for matchin MPIDR values.
- When accessing redistributor registers, index into the array based on
current logical core id.
- On single core configurations these arrays only have one element.