memory: omap-gpmc: Implement IRQ domain for NAND IRQs

GPMC provides 2 interrupts for NAND use. i.e. fifoevent and termcount.
Use IRQ domain for this. NAND device tree node can then
get the necessary interrupts by using gpmc as the interrupt parent.

Legacy boot uses gpmc_get_client_irq to get the
NAND interrupts from the GPMC IRQ domain.
Get rid of custom bitmasks and use IRQ domain for that
as well.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Tony Lindgren <tony@atomide.com>

Documentation/devicetree/bindings/bus/ti-gpmc.txt

@@ -32,6 +32,12 @@ Required properties:
 			bootloader) are used for the physical address decoding.
 			As this will change in the future, filling correct
 			values here is a requirement.
+ - interrupt-controller: The GPMC driver implements and interrupt controller for
+			the NAND events "fifoevent" and "termcount".
+			The interrupt number mapping is as follows
+			0 - NAND_fifoevent
+			1 - NAND_termcount
+ - interrupt-cells:	Must be set to 2
 
 Timing properties for child nodes. All are optional and default to 0.
 
@@ -130,6 +136,8 @@ Example for an AM33xx board:
 		#address-cells = <2>;
 		#size-cells = <1>;
 		ranges = <0 0 0x08000000 0x10000000>; /* CS0 @addr 0x8000000, size 0x10000000 */
+		interrupt-controller;
+		#interrupt-cells = <2>;
 
 		/* child nodes go here */
 	};