drm/xe/guc: Prefer GT oriented messages in xe_guc_pc

If possible, we should prefer xe_gt_err() over drm_err().
While at it, improve and fix some of the error messages.
Also drop unnecessary "xe_gt_sysfs.h" include.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240609181931.1724-4-michal.wajdeczko@intel.com