x86: Look for IA32_ENERGY_PERF_BIAS support

The new IA32_ENERGY_PERF_BIAS MSR allows system software to give
hardware a hint whether OS policy favors more power saving,
or more performance.  This allows the OS to have some influence
on internal hardware power/performance tradeoffs where the OS
has previously had no influence.

The support for this feature is indicated by CPUID.06H.ECX.bit3,
as documented in the Intel Architectures Software Developer's Manual.

This patch discovers support of this feature and displays it
as "epb" in /proc/cpuinfo.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
LKML-Reference: <alpine.LFD.2.00.1006032310160.6669@localhost.localdomain>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>