tools/power turbostat: Validate RAPL MSRs for AWS Nitro Hypervisor

Even though the platform->plat_rapl_msrs enumeration may be accurate,
a VM, such as AWS Nitro Hypervisor, may deny access to the underlying MSRs.

Probe if PKG_ENERGY is readable and non-zero.
If no, ignore all RAPL MSRs.

Reported-by: Emily Ehlert <ehemily@amazon.de>
Tested-by: Emily Ehlert <ehemily@amazon.de>
Signed-off-by: Len Brown <len.brown@intel.com>

Author: lenb