drm/i915: Factor out function to get/put AUX_IO power for main link

drm/i915: Factor out function to get/put AUX_IO power for main link

Factor out functions to get/put the AUX_IO power domain for the main
link on DDI ports.

While at it clarify the corresponding code comment.

No functional change.

v2:
- s/(get/put)_aux_power_for_main_link/main_link_aux_power_domain_(get/put)
  (Jani)
- Clarify in the code comment that AUX_IO is needed only by TypeC besides
  eDP/PSR.
v3:
- Rebased on checking intel_encoder_can_psr() instead of crtc->has_psr.
v4:
- Don't call fetch_and_zero() with side-effect during variable
  declaration. (Ville)

Cc: Jani Nikula <jani.nikula@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/20221114122251.21327-9-imre.deak@intel.com