dt-bindings: hwlock: add sun6i_hwspinlock

Adds documentation on how to use the sun6i_hwspinlock driver for sun6i
compatible series SoCs.

Reviewed-by: Samuel Holland <samuel@sholland.org>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Signed-off-by: Wilken Gottwalt <wilken.gottwalt@posteo.net>
Link: https://lore.kernel.org/r/b7a1f5532e0ae474473858055fd9bbabff9e1449.1615713499.git.wilken.gottwalt@posteo.net
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>