Add tool to copy files in to fat16 images

fat16copy.py can be used to copy files or directories in to the root of
a fat16 image.

Usage: fat16copy <image> <file> [<file> ...]

Test: Used to compose a Raspberry Pi 3 boot image
Bug: 28912590
Change-Id: I29c9eec3786e2c5cc94f9a160360bac850809a93
diff --git a/core/config.mk b/core/config.mk
index c04e660..f04947d 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -585,6 +585,7 @@
 TUNE2FS := $(HOST_OUT_EXECUTABLES)/tune2fs$(HOST_EXECUTABLE_SUFFIX)
 JARJAR := $(HOST_OUT_JAVA_LIBRARIES)/jarjar.jar
 DATA_BINDING_COMPILER := $(HOST_OUT_JAVA_LIBRARIES)/databinding-compiler.jar
+FAT16COPY := build/tools/fat16copy.py
 
 ifneq ($(ANDROID_JACK_EXTRA_ARGS),)
 JACK_DEFAULT_ARGS :=