drm/i915: Fix TypeC mode initialization during system resume

During system resume DP MST requires AUX to be working already before
the HW state readout of the given encoder. Since AUX requires the
encoder/PHY TypeC mode to be initialized, which atm only happens during
HW state readout, these AUX transfers can change the TypeC mode
incorrectly (disconnecting the PHY for an enabled encoder) and trigger
the state check WARNs in intel_tc_port_sanitize().

Fix this by initializing the TypeC mode earlier both during driver
loading and system resume and making sure that the mode can't change
until the encoder's state is read out. While at it add the missing
DocBook comments and rename
intel_tc_port_sanitize()->intel_tc_port_sanitize_mode() for consistency.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220922172148.2913088-1-imre.deak@intel.com