Revert "Remove Krait from cortex-a15 (Test)"

This reverts commit 640991a402f50d7fa23cc05b81d017d207b500f2.
Revert "Optimize for krait cpu's with krait2 clang flags"

This reverts commit 83a553162d71fc086e12d175032b5d53e4b2a3aa.