dt-bindings: add defines for i.MX8MN power domains

The i.MX8M Nano has a similar power domain controller to that of the
mini, but it isn't fully compatible, so it needs a separate binding
and power domain tables.

Add the bindings and tables.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>