drm/xe/gt_throttle: Always read and mask

drm/xe/gt_throttle: Always read and mask

Use a single function to read and mask the value the callers will be
interested in. This reduces the risk of a caller using a plain call to
xe_gt_throttle_get_limit_reasons() without applying any mask, which can
return unexpected bits for future platforms.

Select which reg and mask it's going to be used according to the
platform and gt type and always use that one function.

There was an odd xe_gt_dbg() when reading the status, which is not done
for any other throttle/* sysfs file, so just make the status be as
special as everybody else.

Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Link: https://patch.msgid.link/20251029-gt-throttle-cri-v3-3-d1f5abbb8114@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>