irqchip: irq-dove: Add PMU interrupt controller.

Dove has a Power Management Unit with its own interrupt
controller. This is chained on the main interrupt controller.  Add a
driver, making use of generic chip where possible.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>

cc: devicetree@vger.kernel.org
cc: pawel.moll@arm.com
cc: mark.rutland@arm.com
cc: swarren@wwwdotorg.org
cc: ian.campbell@citrix.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>