structured extended feature flags require eax = 7; avoids incorrectly
detecting avx2 on some older processors that support avx.
from [1]:
INPUT EAX = 0: Returns CPUID’s Highest Value for Basic Processor
Information and the Vendor Identification String
[1] http://www.intel.com/content/www/us/en/processors/processor-identification-cpuid-instruction-note.html
Change-Id: I6b4735b5f7b7729a815e428fca767d1e5a10bcab