drm/i915: Add support for enabling link status and recovery

In this patch enables support for detecting link failures between
PCON and HDMI sink in i915 driver. HDMI link loss indication to
upstream DP source is indicated via IRQ_HPD. This is followed by
reading of HDMI link configuration status (HDMI_TX_LINK_ACTIVE_STATUS).
If the PCON → HDMI 2.1 link status is off; reinitiate frl link
training to recover. Also, report HDMI FRL link error count range for
each individual FRL active lane is indicated by
DOWNSTREAM_HDMI_ERROR_STATUS_LN registers.

v2: Checked for dpcd read and write failures and added debug message.
(Uma Shankar)

v3: Rearranged code to re-start FRL link training or fall back to
TMDS mode.

v4: Resused function to check frl which inturn restarts FRL and
fallback to TMDS mode.

Signed-off-by: Swati Sharma <swati2.sharma@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com> (v2)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201218103723.30844-12-ankit.k.nautiyal@intel.com