drivers/video: fsl-diu-fb: remove unused panel operating mode support

The MFB_TYPE_xxx macros indicate different "operating modes" of each AOI,
but this feature is not actually used in the driver.  The mfb_index.type
field is always set to MFB_TYPE_OUTPUT, so just delete it and any code
that references it.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>