Add function to extract timestamp from boot image

Also add toybox to otatools list.

Bug: 169169031
Test: build OTA
Change-Id: Ib14dbf46a8385ccf2a9c5a9c6f4e7fa9399cf0ba
diff --git a/core/Makefile b/core/Makefile
index 26f11a4..18d901c 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -3887,6 +3887,7 @@
   signapk \
   simg2img \
   sload_f2fs \
+  toybox \
   tune2fs \
   unpack_bootimg \
   update_host_simulator \