Since kernel version 4.7, processor frequency information is available
on S390. Let's adjust the parser so this information shows up for virsh
nodeinfo:

    # virsh nodeinfo
    CPU model:           s390x
    CPU(s):              8
    CPU frequency:       5000 MHz
    CPU socket(s):       1
    Core(s) per socket:  8
    Thread(s) per core:  1
    NUMA cell(s):        1
    Memory size:         16273908 KiB
Reviewed-by: NMarc Hartmayer <mhartmay@linux.vnet.ibm.com>
Reviewed-by: NBoris Fiuczynski <fiuczy@linux.vnet.ibm.com>
Signed-off-by: NBjoern Walk <bwalk@linux.vnet.ibm.com>