android: simplify the subdirs including rules

Use the macro defined in the Android build system.

Signed-off-by: Chih-Wei Huang <cwhuang@linux.org.tw>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/Android.mk b/Android.mk
index e190f74..87ed464 100644
--- a/Android.mk
+++ b/Android.mk
@@ -94,7 +94,6 @@
 SUBDIRS += src/gallium
 endif
 
-mkfiles := $(patsubst %,$(MESA_TOP)/%/Android.mk,$(SUBDIRS))
-include $(mkfiles)
+include $(call all-named-subdir-makefiles,$(SUBDIRS))
 
 endif