V4L/DVB (11840): change kmalloc to vmalloc for sglist allocation in videobuf_dma_map/unmap

Change kmalloc()/kfree() to vmalloc()/vfree() for sglist allocation
during videobuf_dma_map() and videobuf_dma_unmap()

High resolution sensors might require too many contiguous pages
to be allocated for sglist by kmalloc() during videobuf_dma_map()
(i.e. 256Kib for 8MP sensor).
In such situations, kmalloc() could face some problem to find the
required free memory. vmalloc() is a safer solution instead, as the
allocated memory does not need to be contiguous.

Signed-off-by: David Cohen <david.cohen@nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/video4linux/CARDLIST.em28xx

@@ -62,3 +62,5 @@
  64 -> Easy Cap Capture DC-60                   (em2860)
  65 -> IO-DATA GV-MVP/SZ                        (em2820/em2840) [04bb:0515]
  66 -> Empire dual TV                           (em2880)
+ 67 -> Terratec Grabby                          (em2860)        [0ccd:0096]
+ 68 -> Terratec AV350                           (em2860)        [0ccd:0084]