MAINTAINERS: Add Dmitry as MSM DRM driver co-maintainer

MAINTAINERS: Add Dmitry as MSM DRM driver co-maintainer

For the past several releases I have been assisting Rob by writing,
collecting, testing and integrating patches for non-GPU and non-core
parts of MSM DRM driver, while Rob is more interested in improving the
GPU-related part. Let's note this in the MAINTAINERS file.

While we are at it, per Rob's suggestion let's also promote Abhinav
Kumar to M: (as he is actively working on the driver) and switch Sean
Paul to R: (since he isn't doing much on msm these days).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Rob Clark <robdclark@gmail.com>
Link: https://lore.kernel.org/r/20220429215324.3729441-1-dmitry.baryshkov@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>