dt-bindings: serial: fsl-lpuart: add optional power-domains property

Add optional power-domains property for i.MX8 usage.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230328054355.1973397-1-peng.fan@oss.nxp.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>