staging: nvec: ps2: add some more debug functions

This can print the mouse traffic which goes over the i2c bus. Make
mouse debugging messages configurable and disable them by default.

Signed-off-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Julian Andres Klode <jak@jak-linux.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>