dt-bindings: regulator: add pca9450: Add regulator-allowed-modes

dt-bindings: regulator: add pca9450: Add regulator-allowed-modes

Make the PWM mode on the buck controllers configurable from devicetree.
Some boards require forced PWM mode to keep the supply ripple within
acceptable limits under light load conditions.

Signed-off-by: Martijn de Gouw <martijn.de.gouw@prodrive-technologies.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20250525071823.819342-1-martijn.de.gouw@prodrive-technologies.com
Signed-off-by: Mark Brown <broonie@kernel.org>