drm/xe/hwmon: Refactor xe hwmon

Check latest platform first in xe_hwmon_get_reg.
Move PVC HWMON registers to regs/xe_pcode.h.

Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Karthik Poosa <karthik.poosa@intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240201180600.434822-1-karthik.poosa@intel.com