tools/power turbostat: decode MSR_IA32_MISC_ENABLE only on Intel

otherwise, turbostat bails on on AMD Opteron boxes:

turbostat: cpu26: msr offset 0x1a0 read failed: Input/output error

Reported-by: Kamil Kolakowski <kkolakow@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>