drm/msm/dp: power off DP phy at suspend

Normal DP suspend operation contains two steps, display off followed
by dp suspend, to complete system wide suspending cycle if display is
up at that time. In this case, DP phy will be powered off at display
off. However there is an exception case that depending on the timing
of dongle plug in during system wide suspending, sometimes display off
procedure may be skipped and dp suspend was called directly. In this
case, dp phy is stay at powered on (phy->power_count = 1) so that at
next resume dp driver crash at main link clock enable due to phy is
not physically powered on. This patch will call dp_ctrl_off_link_stream()
to tear down main link and power off phy at dp_pm_suspend() if main link
had been brought up.

Changes in V2:
-- stashed changes into dp_ctrl.c
-- add is_phy_on to monitor phy state

Changes in V3:
-- delete is_phy_on
-- call dp_ctrl_off_link_stream() from dp_pm_suspend()

Changes in V4:
-- delete changes made at dp_power.c
-- move main link status checking to dp_pm_suspend

Changes in V5:
-- correct commit id at Fixes tag

Fixes: 8dbde399044b ("drm/msm/dp: handle irq_hpd with sink_count = 0 correctly)
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Tested-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/1622734846-14179-1-git-send-email-khsieh@codeaurora.org
Signed-off-by: Rob Clark <robdclark@chromium.org>