drm/i915/display: Extract separate AUX PW descriptors

drm/i915/display: Extract separate AUX PW descriptors

In an upcoming change, we will fix an ordering issue between PICA and
AUX power wells for Xe2_LPD and later, making sure that the driver
acquires PICA power before AUX.  As a preparation for that, let's
extract separate descriptors for AUX power wells.

Suggested-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20251001-pica-power-before-aux-v2-1-6308df4de5a8@intel.com
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>