Android.bp: Add include exports for android dir

This forward ports Stefan Schake's patch
32ee9c0e0566 "android: Add missing include exports" to the
Android.bp file.

Change-Id: Ie07582b87ae3bda0d49073c524e5c0a394e614bb
Signed-off-by: John Stultz <john.stultz@linaro.org>
diff --git a/Android.bp b/Android.bp
index 429c22c..9121068 100644
--- a/Android.bp
+++ b/Android.bp
@@ -54,7 +54,7 @@
         "libdrm_sources",
     ],
 
-    export_include_dirs: ["include/drm"],
+    export_include_dirs: ["include/drm", "android"],
 
     cflags: [
         "-Wno-enum-conversion",