Some socs have a large number of interrupts requests to service
the needs of its many peripherals and subsystems. All of the
interrupt lines from the subsystems are not needed at the same
time, so they have to be muxed to the irq-controller appropriately.
In such places a interrupt controllers are preceded by an CROSSBAR
that provides flexibility in muxing the device requests to the controller
inputs.

This driver takes care a allocating a free irq and then configuring the
crossbar IP as a part of the mpu's irqchip callbacks. crossbar_init should
be called right before the irqchip_init, so that it is setup to handle the
irqchip callbacks.

Cc: Thomas Gleixner
Cc: Linus Walleij
Cc: Santosh Shilimkar
Cc: Russell King
Cc: Tony Lindgren
Cc: Rajendra Nayak
Cc: Marc Zyngier
Cc: Grant Likely
Cc: Rob Herring
Signed-off-by: Sricharan R
Acked-by: Kumar Gala (for DT binding portion)
Acked-by: Santosh Shilimkar
Acked-by: Linus Walleij
Acked-by: Thomas Gleixner