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 <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Signed-off-by: Imre Deak <[email protected]>
Reviewed-by: José Roberto de Souza <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

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