ARM: OMAP2+: display: Create omapvrfb and omapfb devices inside omap_display_init

Move omapfb and omapvrfb device creation inside the omap_display_init so that
we can correctly create the device based on the presence of omapdss within the
platform.

For example, on a kernel image supporting multiple platforms, omap_init_vrfb and
omap_init_fb will create omapvrfb and omapfb platform devices respectively on a
AM33xx platform even though it doesn't have a VRFB or DSS block.

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