util: virhostcpu: parse frequency information on S390

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>

src/util/virhostcpu.c

@@ -600,6 +600,8 @@ virHostCPUParseFrequency(FILE *cpuinfo,
         prefix = "cpu MHz";
     else if (ARCH_IS_PPC(arch))
         prefix = "clock";
+    else if (ARCH_IS_S390(arch))
+        prefix = "cpu MHz dynamic";
 
     if (!prefix) {
         VIR_WARN("%s is not supported by the %s parser",