Move the bell into an OS function, and use that if it's declared; else,
fall back to using the driver's function.
Remove the Linux keyboard bell function; just move it into the OS layer.
Use named initialisers when converting the old structures, and eliminate
unused functions.
Add KdOsAddInputDrivers, which adds all relevant input drivers.
Could possibly be refactored to KdAddInputDrivers, which called through
OsFuncs to a new function, if it existed.