tools / turbostat: servers do not support uncore power register

From the Intel Software Developer's Manual section 14.7.4,

"For server platforms, PP1 domain is not supported, but its PP0 domain
supports the MSR_PP0_PERF_STATUS interface."

When I run 'turbostat ls' I see the following error:

/dev/cpu/0/msr offset 0x641 read failed

because the server doesn't support the MSR_PP1_ENERGY_STATUS
register (0x641).  This patch implements a get_msr_nowarn()
which suppresses the above warning and then sets !RAPL_GFX.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Merge branch 'pm-tools-next' into bleeding-edge

* pm-tools-next:
  tools / turbostat: servers do not support uncore power register