vulkan: Build hal; minimal stub

bug: 117932393

Just get the HAL building, and make sure Android Vulkan loader can get
to CreateInstance.

Change-Id: I31e1b739a6a0de12b4e47deeec6547ddf46570ee
diff --git a/Android.mk b/Android.mk
index be7551e..39b8144 100644
--- a/Android.mk
+++ b/Android.mk
@@ -135,4 +135,6 @@
 
 include $(GOLDFISH_OPENGL_PATH)/system/egl/Android.mk
 
+include $(GOLDFISH_OPENGL_PATH)/system/vulkan/Android.mk
+
 endif