media: dt-bindings: adv7180: Document the 'interrupts' property

The ADV7180 family of chips have an INTRQ pin that can be connected
to a SoC GPIO.

Allow the 'interrupts' property to be described to fix the following
dt-schema warning:

'interrupt-parent', 'interrupts' do not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>