util: Add MBA check to virResctrlInfoGetCache

util: Add MBA check to virResctrlInfoGetCache

If we have some membw_info data, then we need to calculate the number
of MBA controllers on the system. The value cannot be obtained from a
direct query to the RDT kernel module, but it is the same as the last
level cache value which is calculated by traversing the cache hierarchy
of host(/sys/bus/cpu/devices/cpuX/cache/).

Signed-off-by: Bing Niu <bing.niu@intel.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>