sim: build: hoist lists of hw devices up

sim: build: hoist lists of hw devices up

We need these in the top-level to generate libsim.a, but also in the
subdirs to generate hw-config.h.  Move it to the local.mk, and pass
it down when running recursive make.  This avoids duplication, and
makes it available to both.  We can simplify this once we move the
various steps up to the top-level too.