dt-bindings: remoteproc: imx_rproc: Add minItems for power-domain

"fsl,imx8qxp-cm4" and "fsl,imx8qm-cm4" need minimum 2 power domains. Other
platform doesn't require 'power-domain'.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20240610151721.274424-1-Frank.Li@nxp.com


Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>