AMDGPU/Utils - cleanup include and forward declarations. NFC.

Remove unused includes + forward declarations.
Reduce unnecessary StringRef.h includes to StringRef forward declaration.

Author: RKSimon

llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h

@@ -12,7 +12,6 @@
 #include "AMDGPU.h"
 #include "AMDKernelCodeT.h"
 #include "SIDefines.h"
-#include "llvm/ADT/StringRef.h"
 #include "llvm/IR/CallingConv.h"
 #include "llvm/MC/MCInstrDesc.h"
 #include "llvm/Support/AMDHSAKernelDescriptor.h"
@@ -26,17 +25,13 @@
 namespace llvm {
 
 class Argument;
-class AMDGPUSubtarget;
-class FeatureBitset;
 class Function;
 class GCNSubtarget;
 class GlobalValue;
-class MCContext;
 class MCRegisterClass;
 class MCRegisterInfo;
-class MCSection;
 class MCSubtargetInfo;
-class MachineMemOperand;
+class StringRef;
 class Triple;
 
 namespace AMDGPU {

llvm/lib/Target/AMDGPU/Utils/AMDGPUPALMetadata.h

@@ -14,16 +14,12 @@
 #ifndef LLVM_LIB_TARGET_AMDGPU_AMDGPUPALMETADATA_H
 #define LLVM_LIB_TARGET_AMDGPU_AMDGPUPALMETADATA_H
 
-#include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/MsgPackDocument.h"
-#include <map>
 
 namespace llvm {
 
-class AMDGPUTargetStreamer;
-class formatted_raw_ostream;
-class MCStreamer;
 class Module;
+class StringRef;
 
 class AMDGPUPALMetadata {
   unsigned BlobType = 0;