drm/i915/lspcon: Fix resume time initialization due to unasserted HPD

drm/i915/lspcon: Fix resume time initialization due to unasserted HPD

During system resume time initialization the HPD level on LSPCON ports
can stay low for an extended amount of time, leading to failed AUX
transfers and LSPCON initialization. Fix this by waiting for HPD to get
asserted.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99178
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1485509961-9010-3-git-send-email-imre.deak@intel.com
(cherry picked from commit 390b4e00241ce14ca3967c4698c8f6a158c5a674)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>