ANDROID: GKI: enable CONFIG_VIDEO_V4L2_SUBDEV_API

It's needed by drivers that some boards need, so build it into the
kernel core for everyone to use.

Bug: 162449887
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Id486baec2f3c5b5dfbf18352d940dcf4ac701b67