[SKX] Enabling SKX target and AVX512BW, AVX512DQ, AVX512VL features.

Enabling HasAVX512{DQ,BW,VL} predicates.
Adding VK2, VK4, VK32, VK64 masked register classes.
Adding new types (v64i8, v32i16) to VR512.
Extending calling conventions for new types (v64i8, v32i16)

Patch by Zinovy Nis <zinovy.y.nis@intel.com>
Reviewed by Elena Demikhovsky <elena.demikhovsky@intel.com>

llvm-svn: 213545