sim: hw: rework configure option & device selection

sim: hw: rework configure option & device selection

The sim-hardware configure option allows builders to select a set of
device models to enable.  But this seems like unnecessary overkill:
the existence of individual device models doesn't affect performance
at all as they are only enabled at runtime if the config uses them,
and individually these are all <5KB a piece.  Stripping off a total
of ~50KB from a ~1MB binary doesn't seem useful, and it's extremely
unlikely anyone will ever bother.

So let's simplify the configure/make logic by turning sim-hardware
into a boolean option like many of the other sim options.  Any ports
that have unique device models will declare them in their Makefile
instead of at configure time.  This will allow us to (eventually)
unify the setting into the common dir.