OMAPFB: remove remaining OMAP arch checks

Now that the old omapfb driver is only omap1 display driver, there's no
need to check if the arch is omap1. This patch removes the few remaining
checks for the arch.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>