OMAP: camera code cleanups and compilation fixes

- Fixed the Makefile: camera_core should be compiled only for OMAP1, and in
  conjunction with omap16xxcam.c.
- Fixed the sensor->init() calls and prototype in camera_core.c and
  sensor_ov9640.c.
- Ported the code to the new videobuf code.
- Renamed camera_sensor to omap_camera_sensor since this is an OMAP-specific
  structure.

Signed-off-by: Samuel Ortiz <samuel.ortiz@solidboot.com>
Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>