[media] dt: bindings: Add binding documentation for sunxi IR controller

This patch adds documentation for Device-Tree bindings for sunxi IR
controller.

Signed-off-by: Alexander Bersenev <bay@hackerdom.ru>
Signed-off-by: Alexsey Shestacov <wingrime@linux-sunxi.org>
[hdegoede@redhat.com: Changed compatible to sun4i-a10-ir]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>