ppc32: Update PowerMac "mesh" driver.

Adapt to "macio" driver infrastructure, cleanup power management, make some
functions static, fix IO accessors, remove local list of commands/directions,
etc...

This driver could use more work & study of the interesting ASIC bugs
documented in Apple source code...

Note that I'm removing support for the CHRP machines using the MESH as
part of the "Hydra" ASIC. Nobody sane really uses that, but if one of
the 3 remaining  Longtrail users want to fix that, then move Hydra to
use the "macio" model...