platform/x86/intel/sdsi: Add attribute to read the current meter state

platform/x86/intel/sdsi: Add attribute to read the current meter state

The meter_certificate file provides access to metering information that may
be attested but is only updated every 8 hours. Add new attribute,
meter_current, to allow reading an untested snapshot of the current values.

Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240411025856.2782476-5-david.e.box@linux.intel.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>