video i.MX IPU: Fix display connections

The IPU internally works on 32bit colors. It can arbitrarily map
between pixel formats and internal representation and also between
internal representation and the physical connection to the display.
The driver used to change the mapping between internal representation
and display connection depending on the user selected bpp which is
wrong. Instead, the mapping is specified by the hardware, so an
additional field in platform data is added to describe the connection
between i.MX and the display. The default for this field is RGB666
which seems to be the only configuration which works without this
patch, so I assumed that all in Kernel boards are connected this
way.
This patch has been tested on a RGB666 connected display and a
RGB888 connected display in both 16bpp and 32bpp modes.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>