Zero high 128b YMM registers to avoid SSE-AVX transition penalties

Documents:
- https://software.intel.com/en-us/articles/intel-avx-state-transitions-migrating-sse-code-to-avx
- https://software.intel.com/sites/default/files/m/d/4/1/d/8/11MC12_Avoiding_2BAVX-SSE_2BTransition_2BPenalties_2Brh_2Bfinal.pdf

Change-Id: I90f85fcb15a7a2c49ee068300be6ffe9c68d371c
7 files changed