fbcon: Only allow FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER if fbdev is builtin

Having FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER with fbdev+fbcon being build
as a module does not make much sense.

Having FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER only when fbdev+fbcon are
builtin was always the intention, hence the =y checks but they were
checking the wrong option, fbcon is build as part of fb.ko, so we must
check for FB=y.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>