to prepare for if_media, and to support EISA 3c59x cards:
* change epconfig() to take a short that encodes the chipset
type (3c509, or Demon/Vortex/Boomerang).
* add distinct 3c509 and Demon/Vortex/Boomerang media-sense
functions to back end.
* Add EISA match/attach support for the 3c592 and 3c597
(Demon) cards as well as the 3c509-comatibl EISA 3c509/3c579.
* Assume that ISA and ISA PnP cards are 3c509-style, until
proof to the contrary (e.g. large packet support).
Tested on 3c595, 3c590, and 3c509b. Not tested on 3c515 or Demon.
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