drm/i915: Keep the TypeC port mode fixed for detect/AUX transfers

We must keep the TypeC port mode fixed for the duration of the connector
detection and each AUX transfers. Add a new TypeC lock holding it around
these two sequences. For consistency also hold the lock during the port
mode sanitization.

Whenever resetting the port mode (only during the detection for now) the
port's AUX power domain must be disabled already. Flush the async power
domain disabling work to ensure this.

A follow-up patch will make the port mode changing more robust by
postponing the change for active ports.

v2:
- Fix checkpatch issue: missing annotation for tc_lock.

Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
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/20190628143635.22066-15-imre.deak@intel.com