platform/x86/intel-uncore-freq: Use generic helpers for current frequency

platform/x86/intel-uncore-freq: Use generic helpers for current frequency

Use the generic sysfs helpers for reading the current frequency also,
and remove the custom ones.

No functional change intended.

Signed-off-by: Tero Kristo <tero.kristo@linux.intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://lore.kernel.org/r/20240617060708.892981-8-tero.kristo@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>