V4L/DVB (7196): Lift videobuf-dma-sg's PCI dependency, until it is fixed

videobuf-dma-sg.c should be converted to the generic DMA API to make it
also useful for non-PCI configurations. Even now it can be used thanks
to compatibility macros in include/asm-generic/pci-dma-compat.h. This
has been verified to work on PXA270 CPU with the pxa_camera.c soc-camera
driver. For this the following temporary work-around is needed.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>