The core driver can now operate in either vmalloc or dma-contig modes;
obviously the latter is preferable when it is supported.  Default is
currently vmalloc on all platforms; load the module with buffer_mode=1 for
contiguous DMA mode.
Signed-off-by: NJonathan Corbet <corbet@lwn.net>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>