drm/msm: Add CONTEXT_SWITCH_CNTL bitfields

Add missing bitfields to CONTEXT_SWITCH_CNTL in a6xx.xml.

Tested-by: Rob Clark <robdclark@gmail.com>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8650-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8550-QRD
Tested-by: Neil Armstrong <neil.armstrong@linaro.org> # on SM8450-HDK
Signed-off-by: Antonino Maniscalco <antomani103@gmail.com>
Patchwork: https://patchwork.freedesktop.org/patch/618016/


Signed-off-by: Rob Clark <robdclark@chromium.org>