[media] pwc: Replace private buffer management code with videobuf2

Looking at the pwc buffer management code has made it clear to me it needed
some serious fixing. Not only was there a ton of code duplication even
internally to pwc (read and mmap wait for frame code was duplicated), the
code also was outright buggy. With the worst offender being dqbuf, which
just round robin returned all the mmap buffers, without paying any attention
to them being queued by the app with qbuf or not. And qbuf itself was a noop.

So I set out to fix this and already had some cleanups in place when
I read Jonathan Corbet's lwn article on videobuf2, this inspired me to just
rip out the buffer management code and replace it with videobuf2, greatly
reducing the amount of code, and fixing all bugs in one go:

Many thanks to Jonathan for the timely article on this !

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/pwc/Kconfig

@@ -1,6 +1,7 @@
 config USB_PWC
 	tristate "USB Philips Cameras"
 	depends on VIDEO_V4L2
+	select VIDEOBUF2_VMALLOC
 	---help---
 	  Say Y or M here if you want to use one of these Philips & OEM
 	  webcams:

drivers/media/video/pwc/pwc-ctrl.c

@@ -511,13 +511,9 @@ unsigned int pwc_get_fps(struct pwc_device *pdev, unsigned int index, unsigned i
 	return ret;
 }
 
-#define BLACK_Y 0
-#define BLACK_U 128
-#define BLACK_V 128
-
 static void pwc_set_image_buffer_size(struct pwc_device *pdev)
 {
-	int i, factor = 0;
+	int factor = 0;
 
 	/* for V4L2_PIX_FMT_YUV420 */
 	switch (pdev->pixfmt) {
@@ -541,22 +537,9 @@ static void pwc_set_image_buffer_size(struct pwc_device *pdev)
 	 */
 	pdev->offset.x = ((pdev->view.x - pdev->image.x) / 2) & 0xFFFC;
 	pdev->offset.y = ((pdev->view.y - pdev->image.y) / 2) & 0xFFFE;
-
-	/* Fill buffers with black colors */
-	for (i = 0; i < pwc_mbufs; i++) {
-		unsigned char *p = pdev->image_data + pdev->images[i].offset;
-		memset(p, BLACK_Y, pdev->view.x * pdev->view.y);
-		p += pdev->view.x * pdev->view.y;
-		memset(p, BLACK_U, pdev->view.x * pdev->view.y/4);
-		p += pdev->view.x * pdev->view.y/4;
-		memset(p, BLACK_V, pdev->view.x * pdev->view.y/4);
-	}
 }
 
-
-
 /* BRIGHTNESS */
-
 int pwc_get_brightness(struct pwc_device *pdev)
 {
 	char buf;