[media] vmalloc_sg: make sure all pages in vmalloc area are really DMA-ready

Patch originally written by Konrad. Rebased on current linux media tree.

Under Xen, vmalloc_32() isn't guaranteed to return pages which are really
under 4G in machine physical addresses (only in virtual pseudo-physical
addresses).  To work around this, implement a vmalloc variant which
allocates each page with dma_alloc_coherent() to guarantee that each
page is suitable for the device in question.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: James Harper <james.harper@ejbdigital.com.au>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

include/media/videobuf-dma-sg.h

@@ -53,6 +53,9 @@ struct videobuf_dmabuf {
 
 	/* for kernel buffers */
 	void                *vaddr;
+	struct page         **vaddr_pages;
+	dma_addr_t          *dma_addr;
+	struct device       *dev;
 
 	/* for overlay buffers (pci-pci dma) */
 	dma_addr_t          bus_addr;