media: au0828: fix VIDEO_V4L2 dependency

After the move of videobuf2 into the common directory, selecting the
au0828 driver with CONFIG_V4L2 disabled started causing a link failure,
as we now attempt to build videobuf2 but it still requires v4l2:

ERROR: "v4l2_event_pending" [drivers/media/common/videobuf/videobuf2-v4l2.ko] undefined!
ERROR: "v4l2_fh_release" [drivers/media/common/videobuf/videobuf2-v4l2.ko] undefined!
ERROR: "video_devdata" [drivers/media/common/videobuf/videobuf2-v4l2.ko] undefined!
ERROR: "__tracepoint_vb2_buf_done" [drivers/media/common/videobuf/videobuf2-core.ko] undefined!
ERROR: "__tracepoint_vb2_dqbuf" [drivers/media/common/videobuf/videobuf2-core.ko] undefined!
ERROR: "v4l_vb2q_enable_media_source" [drivers/media/common/videobuf/videobuf2-core.ko] undefined!

We want to be able to build the core au0828 support without V4L2,
so this makes the 'select' conditional on V4L2, and refines the
dependencies in VIDEO_AU0828_V4L2 so it can only be enabled in
the exact conditions that have VIDEOBUF2_VMALLOC reachable.

Fixes: 03fbdb2f ("media: move videobuf2 to drivers/media/common")
Fixes: 05439b1a ("[media] media: au0828 - convert to use videobuf2")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/au0828/Kconfig

@@ -4,7 +4,7 @@ config VIDEO_AU0828
 	depends on I2C && INPUT && DVB_CORE && USB
 	select I2C_ALGOBIT
 	select VIDEO_TVEEPROM
-	select VIDEOBUF2_VMALLOC
+	select VIDEOBUF2_VMALLOC if VIDEO_V4L2
 	select DVB_AU8522_DTV if MEDIA_SUBDRV_AUTOSELECT
 	select MEDIA_TUNER_XC5000 if MEDIA_SUBDRV_AUTOSELECT
 	select MEDIA_TUNER_MXL5007T if MEDIA_SUBDRV_AUTOSELECT
@@ -18,7 +18,8 @@ config VIDEO_AU0828
 
 config VIDEO_AU0828_V4L2
 	bool "Auvitek AU0828 v4l2 analog video support"
-	depends on VIDEO_AU0828 && VIDEO_V4L2
+	depends on VIDEO_AU0828
+	depends on VIDEO_V4L2=y || VIDEO_V4L2=VIDEO_AU0828
 	select DVB_AU8522_V4L if MEDIA_SUBDRV_AUTOSELECT
 	select VIDEO_TUNER
 	default y