[media] v4l: move v4l2 core into a separate directory

Currently, the v4l2 core is mixed together with other non-core drivers.
Move them into a separate directory.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/Kconfig b/drivers/media/Kconfig
index d941581..e625362 100644
--- a/drivers/media/Kconfig
+++ b/drivers/media/Kconfig
@@ -152,6 +152,7 @@
 # Video/Radio/Hybrid adapters
 #
 
+source "drivers/media/v4l2-core/Kconfig"
 source "drivers/media/video/Kconfig"
 
 source "drivers/media/radio/Kconfig"