This patch adds a way to create and use the video plane (YUV overlay) and
scaling video scaling features of the chip.

The overlay is configured, resized and modified using a device specific
ioctl.

Also included in this patch:
  - If no platform data was passed, print an error and exit instead of crashing.
  - Added a write_reg(_dly) macro. This improves readability when
    manipulating chip registers. (no more udelay() after each write).
  - Comments about some issues.

Signed-off-by: Raphael Assenat <raph@8d.com>