fbdev: nvidia: remove the dependency on PPC_OF

The OF functionality has moved to a common place and be used by many
archs. So we don't need to include the ppc arch specific header files
and depend on PPC_OF option any more. This is a preparation for
killing PPC_OF.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>