Revert "AMDGPU/SI: Add amdgpu_kernel calling convention. Part 2."

This reverts commit 47486d52454d60cdf6becc0b2efe533c73794380.

It broke calling OpenCL kernel from another kernel.

llvm-svn: 268739
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h b/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h
index 247837a..2ef3bf5 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h
@@ -29,7 +29,10 @@
   /// Start of implicit kernel args
   unsigned ABIArgOffset;
 
-  bool isKernel() const;
+  bool isKernel() const {
+    // FIXME: Assume everything is a kernel until function calls are supported.
+    return true;
+  }
 
   unsigned ScratchSize;
   bool IsKernel;