V4L/DVB (10571): v4l2-framework.txt: Fixes the videobuf init functions

Documents the driver usage functions, instead of the generic one used
by the videobuf specific handlers.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

Documentation/video4linux/v4l2-framework.txt

@@ -575,9 +575,21 @@ request. The code is generally like this one:
 Those are the videobuffer functions used on drivers, implemented on
 videobuf-core:
 
-- videobuf_queue_core_init()
+- Videobuf init functions
+  videobuf_queue_sg_init()
       Initializes the videobuf infrastructure. This function should be
-  called before any other videobuf function.
+      called before any other videobuf function on drivers that uses DMA
+      Scatter/Gather buffers.
+
+  videobuf_queue_dma_contig_init
+      Initializes the videobuf infrastructure. This function should be
+      called before any other videobuf function on drivers that need DMA
+      contiguous buffers.
+
+  videobuf_queue_vmalloc_init()
+      Initializes the videobuf infrastructure. This function should be
+      called before any other videobuf function on USB (and other drivers)
+      that need a vmalloced type of videobuf.
 
 - videobuf_iolock()
   Prepares the videobuf memory for the proper method (read, mmap, overlay).