libhardware: add separate makefile for modules subdir

Change-Id: I787c444ee1c3a687ee6f8f551c359e5e908ed7f5
Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/modules/Android.mk b/modules/Android.mk
new file mode 100644
index 0000000..a7278bb
--- /dev/null
+++ b/modules/Android.mk
@@ -0,0 +1,2 @@
+hardware_modules := gralloc hwcomposer
+include $(call all-named-subdir-makefiles,$(hardware_modules))