Add a new parameter to pckbc_cnattach(): flags to put in the pckbc bowels.

Add a new parameter to pckbc_cnattach(): flags to put in the pckbc bowels.
For now, only one such flag is defined, PCKBC_CANT_TRANSLATE. It hints
pckbc that the device does not behave correctly to the ``set translation''
commands.

Set this flag if we are running on a Tadpole Ultrabook machine, which needs it.
This makes the built-in keyboard work correctly on this laptop (with the
help of the software translation pckbd diff).

tested & ok kettenis@