MAINTAINERS: Add a separate entry for Qualcomm Adreno GPU drivers

The msm driver is.. gigantic and covers display hardware (incl. things
concerning (e)DP, DSI, HDMI), as well as the entire lineup of Adreno
GPUs (with hw bringup, memory mappings, userspace interaction etc.).

Because of that, people listed as M:/R: receive patches concerning
drivers for any part of the display block OR the GPU. Separate the
latter, as it's both a functionally separate block and is of
interest to different folks.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/590704/
Signed-off-by: Rob Clark <robdclark@chromium.org>