drm/xe/guc: Move GuC power control init to "post-hwconfig"

SLPC is not used at "hwconfig" stage. Move the initialization of data
structures used for SLPC to a later point in probe.
Also - move the xe_guc_pc_init_early to happen just prior to initial
"hwconfig" load.

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240219130530.1406044-3-michal.winiarski@intel.com