drm: adv7511: Add the rgb format flag to adv7511_link_config

Add the rgb format boolean flag to struct adv7511_link_config. This was in
the drm encoder driver, but having it in the adv7511 driver would remove
direct dependency. The flag is copied to the struct adv7511 to be used for
the transmitter configuration.

Signed-off-by: Hyun Kwon <hyunk@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>