media: MAINTAINERS: update the Amlogic VDEC driver maintainer entry

Add myself as co-maintainer of the Amlogic VDEC driver, and add the
missing vdec DT yaml bindings.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>