board: turris: Move Turris Atsha OTP code to separate file

OTP code is not Atsha generic but also it is not Omnia specific. It is
common for all Turris routers which use Atsha cryptochip for storing OTP.
So move this common Turris specific Atsha OTP code from Turris Omnia into
separate file. It will be used also by other Turris routers.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>