- Use named constants for register bits, instead of mystery numebrs
scattered around in the code.
- Use inline functions for bus space read/write, instead of macros
that rely on global variables.
- Move the timecounter struct into the softc instead of treating it
as a global variable. Backlink from it to the softc.
- This leaves a pointer to the softc as the only static/global variable
and it's now used only by DELAY().