Move static helper into ARMTargetLowering. NFC

This exposes the isReadOnly(GlobalValue *) in the ARMTargetLowering so
we can make use of it in GlobalISel as well.

llvm-svn: 312320
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.h b/llvm/lib/Target/ARM/ARMISelLowering.h
index fd93629..40cf545 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.h
+++ b/llvm/lib/Target/ARM/ARMISelLowering.h
@@ -275,6 +275,8 @@
       return (Kind != ScalarCondVectorVal);
     }
 
+    bool isReadOnly(const GlobalValue *GV) const;
+
     /// getSetCCResultType - Return the value type to use for ISD::SETCC.
     EVT getSetCCResultType(const DataLayout &DL, LLVMContext &Context,
                            EVT VT) const override;