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These APIs allow the GIC implementation to categorize interrupt numbers
into SPIs, PPIs, and SGIs. The default implementations for GICv2 and
GICv3 follows interrupt numbering as specified by the ARM GIC
architecture.

API documentation updated.

Change-Id: Ia6aa379dc955994333232e6138f259535d4fa087
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>