Depend on (bs|img)diff for target-files-package

add_img_to_target_files may use these to create the recovery patch, so
add a dependency. They were previously a transitive dependency through
the system image to the standalone recovery patch creation.

Bug: 36575896
Test: rm out/host/linux-x86/bin/imgdiff; m -j target-files-package
Change-Id: I2a43220e94c09393e88e1d9950032f5665a0d2ce