The underlying resctrl monitoring is actually using 64 bit counters,
not the 32bit one. Correct this by using 64bit data type for reading
hardware value.

To keep the interface consistent, the result of CPU last level cache
that occupied by vcpu processors of specific restrl monitor group is
still reported with a truncated 32bit data type. because, in silicon
world, CPU cache size will never exceed 4GB.
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Signed-off-by: NWang Huaqiang <huaqiang.wang@intel.com>