Goals of this new xe_gt_freq component:
1. Detach sysfs controls and raw freq management from GuC SLPC.
2. Create a directory that could later be aligned with devfreq.
3. Encapsulate all the freq control in a single directory. Although
   we only have one freq domain per GT, already start with a numbered
   freq0 directory so it could be expanded in the future if multiple
   domains or PLL are needed.

Note: Although in the goal #1, the raw freq management control is
mentioned, this patch only starts by the sysfs control. The RP freq
configuration and init freq selection are still under the guc_pc, but
should be moved to this component in a follow-up patch.

v2: - Add /tile# to the doc and remove unnecessary kobject_put (Riana)
    - s/ssize_t/int on some ret variables (Vinay)

Cc: Sujaritha Sundaresan <sujaritha.sundaresan@intel.com>
Cc: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Cc: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>