media: dt-bindings: rcar-csi2: List resets as a mandatory property

The resets property will become mandatory to operate the device, list it
as such. All device tree source files have always included the reset
property so making it mandatory will not introduce any regressions.

While at it improve the description for the clocks property.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>