dt-bindings: media: convert imx.txt to yaml format

Convert binding doc imx.txt to yaml format. Create two yaml files:
fsl,imx6-mipi-csi2.yaml and fsl,imx-capture-subsystem.yaml.

Additional changes:
- add example for fsl,imx6-mipi-csi2
- add irq err1 and err2 description
- update MAINTAINERS

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
[hverkuil: drop empty line at the end of the yaml files]