Add a linked list of keyboard handlers.  Added handlers will go
to the head of the list.  Removed handlers will be zapped from
the list.  The head of the list will be used for events.

This fixes the keyboard-dead-after-usb-kbd-unplug issue, key events
will be re-routed to the ps/2 kbd instead of being discarded.

[ v2: fix cut+paste bug found my Markus ]
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Message-id: 1366798118-3248-3-git-send-email-kraxel@redhat.com
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>