video: omap: delete support for early fbmem allocation

Commit 1e434f93

 (OMAPFB: remove early mem
alloc from old omapfb) deleted the support for early fbmem allocation
from the platform code, but some code still remains in the driver side.
Delete this code now, as it repotedly causes build issues on !MMU.

The patch was tested on Amstrad E3 and Nokia 770 and framebuffer
functionality is not affected.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>