Use modedb for initial mode instead of table of few predefined modes.

Add mode_option module parameter as a step toward unification of frame
buffers' parameters.
Signed-off-by: NKrzysztof Helt <krzysztof.h1@wp.pl>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>