x86, cpu: Make init_scattered_cpuid_features() consider cpuid subleaves

Some cpuid features (like xsaveopt) are enumerated using cpuid
subleaves.

Extend init_scattered_cpuid_features() to take subleaf into account.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20100719230205.439900717@sbs-t61.sc.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>