i40e: require SSE4.1 support for vector driver

i40e: require SSE4.1 support for vector driver

Later commits to improve the driver will make use of the SSE4.1
_mm_blend_epi16 intrinsic, so:
* set the compilation level to always have SSE4.1 support,
* and add in a runtime check for SSE4.1 as part of the condition checks
  for vector driver selection.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Zhe Tao <zhe.tao@intel.com>