fix(sys-kernel/coreos-kernel): Fix boot on new ec2 hardware.

Cherry-pick edb6f29464afc65fc73767540b854abf63ae7144 from upstream:
  crypto: xor - Check for osxsave as well as avx in crypto/xor

This fixes booting with old versions of Xen running on new CPUs.
Merge pull request #214 from marineam/avx

fix(sys-kernel/coreos-kernel): Fix boot on new ec2 hardware.