vulkan: move all _Bottom functions

Move them to vulkan::driver namespace and drop the _Bottom suffix.

Change-Id: I47b1639c4074adb9c0658816f5f1e126df7f685b
diff --git a/vulkan/libvulkan/loader.h b/vulkan/libvulkan/loader.h
index de71bc0..fc6b8c2 100644
--- a/vulkan/libvulkan/loader.h
+++ b/vulkan/libvulkan/loader.h
@@ -36,7 +36,7 @@
 const driver::InstanceDriverTable& GetDriverDispatch(VkInstance instance);
 const driver::DeviceDriverTable& GetDriverDispatch(VkDevice device);
 const driver::DeviceDriverTable& GetDriverDispatch(VkQueue queue);
-DebugReportCallbackList& GetDebugReportCallbacks(VkInstance instance);
+driver::DebugReportCallbackList& GetDebugReportCallbacks(VkInstance instance);
 
 }  // namespace vulkan