dt-bindings: arm: actions: Add Sparky

Define a binding for Allo.com Sparky SBC.

Cc: Ioan B. <ioan@allo.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Sudeep Kumar <sudeepkumar@cem-solutions.net>
Signed-off-by: Andreas Färber <afaerber@suse.de>