[AVX512] adding AVXVBMI feature flag

The feature flag is for VPERMB,VPERMI2B,VPERMT2B and VPMULTISHIFTQB instructions. 
More about the instruction can be found in:
hattps://software.intel.com/sites/default/files/managed/07/b7/319433-023.pdf

Differential Revision: http://reviews.llvm.org/D16190

llvm-svn: 258012
diff --git a/llvm/lib/Target/X86/X86Subtarget.cpp b/llvm/lib/Target/X86/X86Subtarget.cpp
index 8ef08c9..739de59 100644
--- a/llvm/lib/Target/X86/X86Subtarget.cpp
+++ b/llvm/lib/Target/X86/X86Subtarget.cpp
@@ -261,6 +261,7 @@
   HasLZCNT = false;
   HasBMI = false;
   HasBMI2 = false;
+  HasVBMI = false;
   HasRTM = false;
   HasHLE = false;
   HasERI = false;