vulkan: add recursive f/n/vulkan/Android.mk

This allows using 'mm' to build everything under this dir, instead of
needing to build in each subdir separately.

Change-Id: I0c7692a7be54899b40f1cacdab3bea0e74d80174
(cherry picked from commit ba85347fc30649a17b00a237d81e8861097baeb9)
diff --git a/vulkan/Android.mk b/vulkan/Android.mk
new file mode 100644
index 0000000..d125673
--- /dev/null
+++ b/vulkan/Android.mk
@@ -0,0 +1 @@
+include $(call all-named-subdir-makefiles, libvulkan nulldrv tools)