media: dt-bindings: media: convert rockchip rga bindings to yaml

Current dts files for Rockchip with 'rga' nodes
are manually verified. In order to automate this process
rockchip-rga.txt has to be converted to yaml.

Changed:
  Add missing reg property

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>