dt-bindings: remoteproc: stm32-rproc: Add firmware-name property

Add the 'firmware-name' property to the remote processor binding
to allow specifying the default firmware name in the device tree.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250327082721.641278-2-arnaud.pouliquen@foss.st.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>