drm/i915: Handle the TCCOLD power-down event

drm/i915: Handle the TCCOLD power-down event

Based on a recent BSpec update (Index/21750) we must handle the TCCOLD
event associated with the DP-alt mode. We can detect this event by
reading an invalid all-1s value from FIA registers.

After detecting TCCOLD we will:
- fall back to TBT-alt mode when attempting to switch to DP-alt mode
- conclude that nothing is connected during live status detection
- WARN when already in unsafe mode, since then TCCOLD is unexpected

v2:
- Use DRM_DEBUG_KMS instead of DRM_DEBUG_DRIVER. (José)
v3:
- Use 0xffffffff instead of -1 as invalid FIA reg value.
  (José, Ville)
- Check for TCCOLD in icl_tc_phy_status_complete() too. (Ville)

Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190628143635.22066-12-imre.deak@intel.com