[media] au0828: remove forced dependency of VIDEO_AU0828 on VIDEO_V4L2

This patch removes the dependendency of VIDEO_AU0828 on VIDEO_V4L2 by
creating a new Kconfig option, VIDEO_AU0828_V4L2, which enables analog
video capture support and depends on VIDEO_V4L2 itself.
With VIDEO_AU0828_V4L2 disabled, the driver will only support digital
television and will not depend on the v4l2-core. With VIDEO_AU0828_V4L2
enabled, the driver will be built with the analog v4l2 support included.
By default, the VIDEO_AU0828_V4L2 option will be set to Y, so as to
preserve the original behavior.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>