drm/xe/guc_pc: Move gt register to the proper place

Move a few defines from xe_guc_pc.c to the right register, now that
there is one: xe_gt_regs.h.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>