[nisimura-pmax-wscons] branch and suggestions from Toru Nisimura:
- Remove bogus tc_slot_info[] name for interrupt handling array
and replace with simplified struct intrhand intrtab[] array.
- Add intr_establish() and intr_disestablish() function pointers
to struct platform and initialise this in each model-specific
initialisation, and remove global tc_enable_interrupt function
pointer.
- Remove model-specific function declarations from ibus/ibusvar.h.
This is functionally identical to the current scheme, and doesn't
yet try to commonise interrupt establishment by bus type as the
[nisimura-pmax-wscons] branch does.
Also, move cpuspeed variable from autoconf.c to machdep.c
bdf420bdbf