MAINTAINERS: make omapfb orphan

omapfb is not maintained by me anymore, so drop my name from the
maintainers, and mark omapfb as orphan.

At some point in the future we should mark omapfb as obsolete, but there
are still some features supported by omapfb which are not supported by
omapdrm, so we're not there yet.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>