chore(gicv2): use interrupt group instead of type

The generic interrupt controller identifies an interrupt based on its
type whereas the GIC uses the notion of groups to identify an
interrupt.

This patch changes the name of the helper functions to use group
rather than type for handling interrupts. No functional change in this
patch.

Change-Id: If13ec65cc6c87c2da73a3d54b033f02635ff924a
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>