Android: fix building of modetest and proptest

These tests depend on tests/util/ headers, but expect the include path
to be tests/.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/Android.mk b/Android.mk
index 5209059..292be23 100644
--- a/Android.mk
+++ b/Android.mk
@@ -24,6 +24,8 @@
 LIBDRM_COMMON_MK := $(call my-dir)/Android.common.mk
 
 LOCAL_PATH := $(call my-dir)
+LIBDRM_TOP := $(LOCAL_PATH)
+
 include $(CLEAR_VARS)
 
 # Import variables LIBDRM_{,H_,INCLUDE_H_,INCLUDE_VMWGFX_H_}FILES