drm/xe/hwmon: Expose input voltage attribute

drm/xe/hwmon: Expose input voltage attribute

Use Xe HWMON subsystem to display the input voltage.

v2:
  - Rename hwm_get_vltg to hwm_get_voltage (Riana)
  - Use scale factor SF_VOLTAGE (Riana)
v3:
  - %s/gt_perf_status/REG_GT_PERF_STATUS/
  - Remove platform check from hwmon_get_voltage()
v4:
  - Fix review comments (Andi)

Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Riana Tauro <riana.tauro@intel.com>
Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://lore.kernel.org/r/20230925081842.3566834-4-badal.nilawar@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>