These functions allocate videobuf_buffer structures only. Renaming in order
to prevent confusion with functions allocating actual video buffer memory.

Rename the functions in videobuf-core.h videobuf-dma-sg.c as well.
Signed-off-by: NPawel Osciak <p.osciak@samsung.com>
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>