media: v4l2_fh.h: add missing kconfig.h include

v4l2_fh.h uses the IS_ENABLED() macro and thus should include kconfig.h.

Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>