media: dt-bindings: mt9p031: Convert bindings to yaml

Convert mt9p031 sensor bindings to yaml schema. Also update the
MAINTAINERS entry.

Although input-clock-frequency and pixel-clock-frequency have not been
definded as endpoint propierties in the textual bindings, the sensor
does parse them from the endpoint. Thus move these properties to the
endpoint in the new yaml bindings.

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>