tools/power turbostat: Validate APERF access for VMWARE

tools/power turbostat: Validate APERF access for VMWARE

VMWARE correctly enumerates lack of APERF and MPERF in CPUID,
but turbostat didn't consult that before attempting to access them.

Since VMWARE allows access, but always returns 0, turbostat
got confusd into an infinite reset loop.

Head this off by listening to CPUID.6.APERF_MPERF
(and rename the existing variable to make this more clear)

Reported-by: David Arcari <darcari@redhat.com>
Tested-by: David Arcari <darcari@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>