Keep the compiled '.bin' file to remove the need to compile it when
flashing. This remove the need to have the toolchain when flashing so
allow compiling and flashing with `BUILD_IN_DOCKER=1` without a local
toolchain.
Even if it ends up storing a binary, the file is only 34 bytes.
With the canned recipe for flashing, flash dependencies should be
added to FLASHDEPS, instead of writing `flash: dependencies`. This
ensures that both flash and flash-only depend on the same prerequisites.
