powerpc/fsl-diu-fb: Support setting display mode using EDID

Adds support for encoding display mode information
in the device tree using verbatim EDID block.

If the EDID entry in the DIU node is present, the
driver will build mode database using EDID data
and allow setting the display modes from this database.
Otherwise display mode will be set using mode
entries from driver's internal database as usual.

This patch also updates device tree bindings.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>