ARM: dts: keystone: Add guestos maintenance interrupt

Update the Keystone gic device tree entry to add the maintenance
interrupt information.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm/boot/dts/keystone.dtsi

@@ -65,6 +65,8 @@
 		      <0x0 0x02562000 0x0 0x2000>,
 		      <0x0 0x02564000 0x0 0x1000>,
 		      <0x0 0x02566000 0x0 0x2000>;
+		interrupts = <GIC_PPI 9 (GIC_CPU_MASK_SIMPLE(4) |
+				IRQ_TYPE_LEVEL_HIGH)>;
 	};
 
 	timer {