arm: GIC: reset the CPU interface before running a new guest

arm: GIC: reset the CPU interface before running a new guest

All pending interrupts need to be cleared before running a new guest.
This patch resets the list registers, the software pending queue, and
the GIC hypervisor config registers.
Since the suspend loop was entered through the IRQ handler, we also need
to deactivate that active IPI.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
[Jan: switch to mmio accessors]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>