[AVX512] Enable FP arithmetic lowering for AVX512VL subsets.
Added RegOp2MemOpTable4 to transform 4th operand from register to memory in merge-masked versions of instructions. 
Added lowering tests.

llvm-svn: 224516
diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index 57b19589..5662e86 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -152,6 +152,7 @@
   RegOp2MemOpTableType RegOp2MemOpTable1;
   RegOp2MemOpTableType RegOp2MemOpTable2;
   RegOp2MemOpTableType RegOp2MemOpTable3;
+  RegOp2MemOpTableType RegOp2MemOpTable4;
 
   /// MemOp2RegOpTable - Load / store unfolding opcode map.
   ///