drm/msm: Update register xml

Sync register xml from mesa commit eb3e0b7164a3 ("freedreno/a6xx: Split
descriptors out into their own file").

Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>
Acked-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/662470/