drm/msm/dp: Add basic PSR support for eDP

Add support for basic panel self refresh (PSR) feature for eDP.
Add a new interface to set PSR state in the sink from DPU.
Program the eDP controller to issue PSR enter and exit SDP to
the sink.

Signed-off-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>
Signed-off-by: Vinod Polimera <quic_vpolimer@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/524734/
Link: https://lore.kernel.org/r/1677774797-31063-10-git-send-email-quic_vpolimer@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>