drm/msm/dp: handle irq_hpd with sink_count = 0 correctly

irq_hpd interrupt should be handled after dongle plugged in and
before dongle unplugged. Hence irq_hpd interrupt is enabled at
the end of the plugin handle and disabled at the beginning of
unplugged handle. Current irq_hpd with sink_count = 0 is wrongly
handled same as the dongle unplugged which tears down the mainlink
and disables the phy. This patch fixes this problem by only tearing
down the mainlink but keeping phy enabled at irq_hpd with
sink_count = 0 handle so that next irq_hpd with sink_count =1 can be
handled by setup mainlink only. This patch also set dongle into D3
(power off) state at end of handling irq_hpd with sink_count = 0.

Changes in v2:
-- add ctrl->phy_Power_count

Changes in v3:
-- del ctrl->phy_Power_count
-- add phy_power_off to dp_ctrl_off_link_stream()

Changes in v4:
-- return immediately if clock disable failed at dp_ctrl_off_link_stream()

Changes in v5:
-- set dongle to D3 (power off) state at dp_ctrl_off_link_stream()

Changes in v6:
-- add Fixes tag

Fixes: ea9f337c

 ("drm/msm/dp: reset dp controller only at boot up and pm_resume")
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/1621635930-30161-1-git-send-email-khsieh@codeaurora.org
Signed-off-by: Rob Clark <robdclark@chromium.org>