Add support for reading the meter certificate from Intel On Demand
hardware.  The meter certificate [1] is used to access the utilization
metrics of enabled features in support of the Intel On Demand consumption
model. Similar to the state certificate, the meter certificate is read by
mailbox command.

While making similar changes also use the BIN_ATTR_ADMIN_RO helper to
create the 'registers' sysfs file.

Link: https://github.com/intel-sandbox/debox1.intel_sdsi/blob/gnr-review/meter-certificate.rst [1]
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Link: https://lore.kernel.org/r/20221119002343.1281885-5-david.e.box@linux.intel.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>