arm: GIC: filter redistributor accesses

arm: GIC: filter redistributor accesses

Since each cell has its own set of CPU ids, they can't access the
redistributor associated to their MPIDR. Instead, the MMIO accesses are
translated to their physical redistributor, and a read to the ID
register returns the virtual affinity value.

It is a bit more expensive than simply mapping the redistributor to the
cell, but the guest rarely needs to reconfigure its PPIs and IPIs, so
this patch shouldn't introduce any significant performance loss.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>