console-setup keymap support

[Samuel Thibault <sthibault@debian.org>]

Hello,

If somebody has time to spend on a small and not-too-hard project,
it would be useful to add gnumach keymap support to console-setup.
It should be mostly a matter of translating the console-setup keyboard
format into the struct kbentry format (from gnumach's kd.h, see kd.c's
key_map array for the default value), opening the kd device (see
pc_kbd_start in hurd/console-client/pc-kbd.c for an example that opens
kbd, simply replace kbd with kd), and call device_set_status(dev,
KDSKBENT, &entry, 2) for each key map definition.

Note: use the kd.h and kd.c from the git repository, I've cleaned them a
bit.

Samuel