drm/msm/dp: return correct connection status after suspend

During suspend, dp host controller and hpd block are disabled due to
both ahb and aux clock are disabled. Therefore hpd plug/unplug interrupts
will not be generated. At dp_pm_resume(), reinitialize both dp host
controller and hpd block so that hpd plug/unplug interrupts will be
generated and handled by driver so that hpd connection state is updated
correctly. This patch will fix link training flaky issues.

Changes in v2:
-- use container_of to cast correct dp_display_private pointer
   at both dp_pm_suspend() and dp_pm_resume().

Changes in v3:
-- replace hpd_state atomic_t  with u32

Changes in v4
-- call dp_display_host_deinit() at dp_pm_suspend()
-- call dp_display_host_init() at msm_dp_display_enable()
-- fix phy->init_count unbalance which causes link training failed

Changes in v5
--  add Fixes tag

Fixes:  8ede2ecc

 (drm/msm/dp: Add DP compliance tests on Snapdragon Chipsets)
Tested-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>