MAINTAINERS: drop myself as maintainer

I will no longer regularly work on this platform. Hence will
step down from maintainer duties.

Also, add Jessica as a reviewer to the MSM DRM subsystem to help
out with the reviews.

Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/655558/


Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>