[X86][AsmParser] Don't allow X86::DX in CheckBaseRegAndIndexRegAndScale.
[X86][AsmParser] Don't allow X86::DX in CheckBaseRegAndIndexRegAndScale.

This was here because out and in instructions allow '(%dx)' even though its not a memory reference. To handle this we build a special operand for the DX register reference before we get to the call to CheckBaseRegAndIndexRegAndScale. So we no longer need this special case.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@350483 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm