media: MAINTAINERS: add entry for STM32 DCMIPP driver

Add the entry related to the STM32 MEDIA DCMIPP driver within the
MAINTAINERS file.
Add myself as maintainer of the DCMI driver as well.

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
[Sakari Ailus: Arrange files alphabetically.]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>