drivers/interrupt_controller: Introduce multi-level interrupt support

In a scenario where a platform harbours multiple interrupts to the
extent the core cannot support it, an interrupt controller is added
as an additional level of interrupt. It typically combines several
sources of interrupt into one line that is then routed to the parent
controller.

Signed-off-by: Rajavardhan Gundi <rajavardhan.gundi@intel.com>