[versatilepb] Fix keyboard driver after switching to upstream DTS

FreeBSD's DTS contained only one PL050 node and driver considered it to
be PS/2 keyboard. In reality PL050 is a PS/2 port that pushes bytes to/from
the periphers connected to it. New DTS contains two nodes and QEMU emulates
keyboard connected to port #0 and mouse connected to port #1. Since there
is no way to say what's connected to port by checking DTS we hardcode
this knowledge in the driver: it assumes keyboard on port #0 and ignores
port #1 altogether.

Also QEMU defaults emulated keyboard to scan code set 2 while driver used
to work with scan code set 1 so when initializing driver make sure keyboard
is switched to scan code set 1