Add preliminary support for Windtunnel PowerMacs to ofpath

Add preliminary support for Windtunnel PowerMacs to ofpath

* CHANGES IN THIS COMMIT ARE PRELIMINARY **DO NOT DISTRIBUTE**

* ofpath: Add preliminary support for Windtunnel PowerMacs
  - If /proc/ide/pmac (perhaps to be renamed) does not exist and
    machine is a Windtunnel return ultra2: instead of hd: (this assumes
    machines without /proc/ide/pmac are also without support for ATA-100,
    ultra2: is the ATA-66 bus).
  - Parse a modified version of /proc/ide/pmac to determine the
    appropriate OpenFirmware device specifier, no kernel yet has the
    correct version of this file.
git-archimport-id: erbenson@alaska.net--public/yaboot--devel--1.3--patch-34