MLK-14399: 4.9 rebase: LVDS panel does not work on iMX6SX Auto

MLK-14399: 4.9 rebase: LVDS panel does not work on iMX6SX Auto

The LCDIF driver fails at boot time because it cannot read display timings
from device tree. This is a fake error because the LCDIF DT node contains a
display device property which leads to the display driver that also provides
the timings.

This fake error case has been introduced by
commit 5443a75ed038 ("MLK-14283: dts: fix DE polarity for lcdif") and
commit 56412d6a83d8 ("MLK-13996: lcdif: Use DE polarity specified in DTS")
which fixed DE polarity panel differences for different boards.

This patch adds support for choosing a particular video mode from the ones
provided by the display driver, thus also fixing the DE polarity issue
initially fixed by the above mentioned 2 patches.

Signed-off-by: Cristina Ciocan <cristina-mihaela.ciocan@nxp.com>