spi: lpspi: Add power-domains to the DT bindings

i.MX8(X) based SoC use a power domain. Allow supplying this domain in
bindings.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230721111020.1234278-2-alexander.stein@ew.tq-group.com


Signed-off-by: Mark Brown <broonie@kernel.org>