usb: gadget: udc: atmel: convert to use GPIO descriptors

Use GPIO descriptors instead of relying on the old method.
Include irq.h header since it is needed and was indirectly
included through of_gpio.h.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>