dt-bindings: power: add Amlogic secure power domains bindings

Add the bindings for the Amlogic Secure power domains, controlling the
secure power domains.

The bindings targets the Amlogic A1 and C1 compatible SoCs, in which the
power domain registers are in secure world.

Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1579087831-94965-3-git-send-email-jianxin.pan@amlogic.com