Instead of exposing inner workings of libps2 to drivers such as atkbd and
psmouse, have them define pre-receive and receive callbacks, and provide a
common handler that can be used with underlying serio port.

While at this add kerneldoc to the module.

Link: https://lore.kernel.org/r/ZGK81cxqjr/KS1kA@google.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>