OMAP: DSS2: OMAPFB: Allow usage of def_vrfb only for omap2,3

VRFB is supported only on OMAP2 and OMAP3 platforms. If VRFB rotation is
not supported by the hardware and the user requests VRFB rotation,
print a warning and ignore the request from the user.

Signed-off-by: Senthilvadivu Guruswamy <svadivu@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>