dt-bindings: serial: stm32: add power-domains property

STM32 serial may be in a power domain.
Allow a single 'power-domains' entry for STM32 serial devices.

Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240118091135.3314330-1-valentin.caron@foss.st.com


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