Input: hid-input - allow mapping unknown usages

Currently HID layer only allows to remap keycodes for known usages,
and responds with -EINVAL when user tries to map new usage code.
This precludes us form relying on udev/keymap for establishing correct
mappings and forces us to write dummy HID drivers responsible only for
setting up keymaps.

Let's allow remapping not only usages that have been set up as keys
(usage->type == EV_KEY) but also yet-unmapped usages (usage->type == 0).

Acked-by: Jarod Wilson <jarod@redhat.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>