A driver is supposed to know what type an LED is, unknown doesn't help anyone
here. So replace this with a private #define and abort when a driver doesn't
set the type. This also adds a requirement that any driver initializing a LED
must have the read_led() function, otherwise we can't fill it in correctly.
And bump the enum up by one, the first valid value should start at 1 (or some
other non-boolean value).
Related #365Fixes#364
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>