The back end GIC driver converts and assigns the interrupt type to
suitable group.

For GICv2, a build option GICV2_G0_FOR_EL3 is introduced, which
determines to which type Group 0 interrupts maps to.

 - When the build option is set 0 (the default), Group 0 interrupts are
   meant for Secure EL1. This is presently the case.

 - Otherwise, Group 0 interrupts are meant for EL3. This means the SPD
   will have to synchronously hand over the interrupt to Secure EL1.

The query API allows the platform to query whether the platform supports
interrupts of a given type.

API documentation updated.

Change-Id: I60fdb4053ffe0bd006b3b20914914ebd311fc858
Co-authored-by: Yousuf A <yousuf.sait@arm.com>
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>