[kbd] add keymap loading for event devices

Good morning,

there's currently no way to easily apply a keymap (given as a keymap 
file) to an event device.

What do you think about adding such a feature to loadkeys? That'd also 
enable udev to easily apply the system keymap to hotplugged event devices.

Keymaps are practically the only thing evdevs keep as global state 
(everything else on a per-fd basis), so you don't need to apply the 
keymap every time you open an evdev. It's sufficient to apply the keymap 
to the evdev once, when it's plugged in - loadkeys would be perfect for 
this.

I'd be willing to contribute if you agree to add this feature to loadkeys.

Best regards,
Hannes Winkler