x86, cpu: Support the features flags in new CPUID leaf 7

Intel has defined CPUID leaf 7 as the next set of feature flags (see
the AVX specification, version 007).  Add support for this new feature
flags word.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <tip-*@vger.kernel.org>