From Bruce Evans: (prototype related changes, other cleanups)

Add prototypes. Use static for function definitions to match existing
prototypes. Otherwise leave functions that should be static as extern.
TODO: declare everthing except sidriver and siintr as static. I use
some new cdevs registration functions to do this for syscons and pcvt.

Fix siintr() to match its prototype in ioconf.c (don't return anything).
This may break the eisa support, but Julian says that eisa interrupts
never worked anyway.

(EISA support was never tested anyway - Peter)

Submitted by: bde