Add lk_bell() to ring keyboard audible bell (for rcons bell).
Add LK_KEY_CLICK option to reset keyboard and enable keyclick.
(off by default since theres no way to control it from userland yet).
* Do rcons output properly, using cn_tab->cn_dev which points
at rcons cdevsw entrypoints.
* The pmadx console code was using keyboard (serial) device
(major,minor) for raster consoles with special code in the keyboard
drivers to catch output intended for consoles, pull it off the device
queue, and print them via cnputc().
Ifdef out RCONS_BRAINDAMAGE.
* Other minor cleanup to pmax scc driver.
from DELAY(100) to DELAY(150). The newer accurate DELAY() calibration
left some mice (mostly VSXXX-GA square, not VSXXX-AA hockeypuck)
ignoring the MOUSE_INCREMENTAL command.
The 150ms delay is verified to work on 3100s on both kinds of mice.
