Add input dependencies to .img targets

They should have build/tools/releasetools/*.py as their
prerequisites.

Bug: 27954979
Change-Id: I51595fc91caaad38be3e47befb5df7ac2683bf14
diff --git a/core/config.mk b/core/config.mk
index e63a135..563bce4 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -563,6 +563,7 @@
 PROGUARD := external/proguard/bin/proguard.sh
 JAVATAGS := build/tools/java-event-log-tags.py
 MERGETAGS := build/tools/merge-event-log-tags.py
+BUILD_IMAGE_SRCS := $(wildcard build/tools/releasetools/*.py)
 APPEND2SIMG := $(HOST_OUT_EXECUTABLES)/append2simg
 VERITY_SIGNER := $(HOST_OUT_EXECUTABLES)/verity_signer
 BUILD_VERITY_TREE := $(HOST_OUT_EXECUTABLES)/build_verity_tree