At least on GICv1 the interrupts 0 up to including 31 are so called
Peripheral Private Interrupts (PPIs). We have to initialize the
priority of the PPIs on secondary processors.
This adds support for the GICv3 interrupt controller along with the
redistributor to control SGIs and PPIs which wasn't present in GICv2
implementations. GICv3 implementations only optionally support
memory-mapped GICC interface interaction and require system register
access be implemented, so the GICC interface is accessed only
through system registers.
The following variants
* GICv1 with Security Extensions,
* GICv2 without Security Extensions, or
* within Secure processor mode
have the ability to assign group 0 or 1 to individual interrupts. Group
0 interrupts can be configured to raise an FIQ exception. This enables
the use of NMIs with respect to RTEMS.
BSPs can enable this feature with the BSP_ARM_GIC_ENABLE_FIQ_FOR_GROUP_0
define. Use arm_gic_irq_set_group() to change the group of an
interrupt (default group is 1, if BSP_ARM_GIC_ENABLE_FIQ_FOR_GROUP_0 is
defined).
