fbdev: do not let CONFIG_FB_DEFERRED_IO default to y

CONFIG_FB_DEFERRED_IO can not be turned off, while it's already selected
automatically by the drivers that need it.

Although it's nice to have more compile-coverage, not being able to disable a
rarely used feature is annoying.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Jaya Kumar <jayakumar.lkml@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>