[CSKY] Adjust includes in MCTargetDesc to avoid unnecessary CodeGen deps, NFC

See issue llvm#64166 for more information about layering.

Author: MaskRay

llvm/lib/Target/CSKY/MCTargetDesc/CSKYTargetStreamer.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "CSKYTargetStreamer.h"
-#include "CSKYSubtarget.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/MC/MCContext.h"