independent TC support in sys/dev/tc/tc.c and sys/dev/tc/tcvar.h:
* Change the tc autoconfiguration tables to use a struct tc_attach_args
instead of the ad-hoc structure.
* Change all pmax device drivers to use a `struct confargs' that's
assignment-compatible with sys/dev/tc/tcvar.h `struct tcdev_attach_args'.
Devices that can be present on a TC or as ioctl asic/mainbus builtins
use the same `struct confargs'.
* Eliminate the `BUS_CVTADDR()' macros which the pmax port inherited from
an old, now-obsolete sys/arch/alpha snapshot.
* Update the comments and debugging code in interrupt handlers to
be consistent with the machine-independent TC support.
Other commits that overlap the same source files include: re-enabling
clock-tick interrupts earlier, and counting hardclock ticks for vmstat -i.
mycroft