adding notion of "hints" to FruDevice

[Patrick Venture]

James;

One difficulty we've run into is the 16-bit address detection can be
flaky.  It's not known yet whether there's some underlying i2c issue
on the board or with the i2c driver that could be leading to the
flakiness, but to get around it I've been forced to add hints to
FruDevice locally.  Effectively, it's a lookup that says, if this is
the bus and address, it's 16-bit.  Sort of a way to say, if something
is in the PE slot (which we know the buses for) then we know it's
16-bit.  It's just an idea of been playing with to get a couple things
working, and I was curious if the notion had larger appeal?

the production-ized idea would be, optional hint json configuration
that does a priority search:
devices
addresses
buses

So it'd search if there was a device match, then search for an address
match, then a bus match, otherwise fall back without a hint to the
dynamic attempt.

It's certainly not a perfect solution.  It requires the system
programmer to enforce that certain cards are only placed in certain
slots -- but it is _optional_...

Patrick