Convert the OmniVision OV7251 Image Sensor binding to DT schema format.

vddd-supply was listed as required, but the example and actual user
don't have it. Also, the data brief says it has an internal regulator,
so perhaps it is truly optional.

Add missing common "link-frequencies" which is used and required by the
Linux driver.
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Wolfram Sang <wsa@kernel.org> # for I2C
Link: https://lore.kernel.org/r/20230817202713.2180195-1-robh@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>