ARM: dts: da850: Add interrupt-controller property to gpio node

The gpio node has 144 gpios. Each gpio is capable of generating
an interrupt. Hence add interrupt-controller property to the gpio
node. With this in place one can use interrupts property in device
tree to request for the gpio interrupts.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>