MAINTAINERS: Promote Frank Li as i.MX7/8 media maintainer

MAINTAINERS: Promote Frank Li as i.MX7/8 media maintainer

Move Rui Miguel Silva to reviewer since he does not have sufficient time to
maintain i.MX7/8 media drivers. Frank Li has the hardware, complete
documentation, and has participated actively in patch review. Promote him
as the i.MX7/8 media drivers maintainer.

Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>