layers: Move code to preferred cpp file

PreCallValidateGetImageSubresourceLayout() from core_validation.cpp
to buffer_validation.cpp

Change-Id: Ic55e049fab28384d30768e8c590f158e603dd343
diff --git a/layers/buffer_validation.h b/layers/buffer_validation.h
index 2769f3d..7970dde 100644
--- a/layers/buffer_validation.h
+++ b/layers/buffer_validation.h
@@ -226,4 +226,6 @@
 void PreCallRecordCmdCopyBufferToImage(layer_data *device_data, GLOBAL_CB_NODE *cb_node, BUFFER_STATE *src_buff_state,
                                        IMAGE_STATE *dst_image_state);
 
+bool PreCallValidateGetImageSubresourceLayout(layer_data *device_data, VkImage image, const VkImageSubresource *pSubresource);
+
 #endif  // CORE_VALIDATION_BUFFER_VALIDATION_H_