HEADSUP: bus_space/resource API improvements.

[Poul-Henning Kamp]

I have committed the new convenience functions for bus_space/resources,
and updated a couple of drivers (pci/if_sis, dev/ieee488, dev/adlink)
to use them.

On average, 10-30 lines of code less is necessary for each device driver
and very often two or more fields from the softc disappear as well.

The changes are MFC'able, but no decision has been taken on this yet.

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