[media] Cleanup media Kconfig files

- get rid of ridden V4L2_COMMON symbol

  This symbol is not needed anymore; it can be folded with V4L2
  one, simplifying the Kconfig a little bit;

- Comment why some Kconfig items are needed;

- Remove if test for MEDIA_CAMERA_SUPPORT, replacing it by
  depends on.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/v4l2-core/Makefile b/drivers/media/v4l2-core/Makefile
index c0e90bc..c2d61d4 100644
--- a/drivers/media/v4l2-core/Makefile
+++ b/drivers/media/v4l2-core/Makefile
@@ -11,7 +11,7 @@
 endif
 
 obj-$(CONFIG_VIDEO_DEV) += videodev.o v4l2-int-device.o
-obj-$(CONFIG_VIDEO_V4L2_COMMON) += v4l2-common.o
+obj-$(CONFIG_VIDEO_V4L2) += v4l2-common.o
 
 obj-$(CONFIG_VIDEO_TUNER) += tuner.o