HID: add driver for U2F Zero built-in LED and RNG

U2F Zero supports custom commands for blinking the LED and getting data
from the internal hardware RNG. Expose the blinking function as a LED
device, and the internal hardware RNG as an HWRNG so that it can be used
to feed the enthropy pool.

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>