drm/i915/tc: Fix system resume MST mode restore for DP-alt sinks

drm/i915/tc: Fix system resume MST mode restore for DP-alt sinks

At least restoring the MST topology during system resume needs to use
AUX before the display HW readout->sanitization sequence is complete,
but on TC ports the PHY may be in the wrong mode for this, resulting in
the AUX transfers to fail.

The initial TC port mode is kept fixed as BIOS left it for the above HW
readout sequence (to prevent changing the mode on an enabled port).  If
the port is disabled this initial mode is TBT - as in any case the PHY
ownership is not held - even if a DP-alt sink is connected. Thus, the
AUX transfers during this time will use TBT mode instead of the expected
DP-alt mode and so time out.

Fix the above by connecting the PHY during port initialization if the
port is disabled, which will switch to the expected mode (DP-alt in the
above case).

As the encoder/pipe HW state isn't read-out yet at this point, check if
the port is enabled based on the DDI_BUF enabled flag. Save the read-out
initial mode, so intel_tc_port_sanitize_mode() can check this wrt. the
read-out encoder HW state.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230316131724.359612-5-imre.deak@intel.com