[SKX] Enabling mask instructions: encoding, lowering
KMOVB, KMOVW, KMOVD, KMOVQ, KNOTB, KNOTW, KNOTD, KNOTQ

Reviewed by Elena Demikhovsky <elena.demikhovsky@intel.com>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213757 91177308-0d34-0410-b5e6-96231b3b80d8