media: ov6650: convert to standalone v4l2 subdevice

Remove the soc_camera dependencies and move the diver to i2c

Lost features, fortunately not used or not critical on test platform:
- soc_camera power on/off callback - replaced with clock enable/disable
  only, no support for platform provided regulators nor power callback,
- soc_camera sense request - replaced with arbitrarily selected default
  master clock rate and pixel clock limit, no support for platform
  requested values,
- soc_camera board flags - no support for platform requested mbus config
  tweaks.

Tested on Amstrad Delta with now out of tree but still locally
maintained omap1_camera host driver.

Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>