drm/msm/dp: Enable ASSR for supported DP sinks

The eDP sink on sc7280 supports ASSR and dp driver will
enable ASSR in the source hardware. The driver needs to
enable the ASSR field in the DPCD configuration register
to avoid screen corruption. This change will enable ASSR
if supported in the sink device.

Signed-off-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/1635839325-401-6-git-send-email-quic_sbillaka@quicinc.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>