media: MAINTAINERS: Add entry for V4L2 async and fwnode frameworks

Add an entry for V4L2 async and fwnode frameworks, with myself as the
maintainer.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>