In the case of platforms where a bios or firmware has not already
assigned all the resources, do so. Requires the platform supply one or
more ranges of physical address space and IO that can be mapped into
BARs.
Handles iterating through bridges, computing the sizes of all the
peripherals downstream and rolling that up as well.
Had to rearrange the proble logic somewhat, but now the bus manager will
assign consequtive bus numbers as it finds bridges and recursively
drills down to discover the entire bus structure.
Does not assign resources yet, but need to do this in the first pass
to find all of the devices before can figure out how much space they
occupy.
