power: regulator: fix dependency for REGULATOR_PWM

power: regulator: fix dependency for REGULATOR_PWM

The PWM regulator driver is a uclass driver, thus requiring DM_PWM to be
enabled to be actually usable (and with the appropriate PWM controller
driver enabled as well, but that we cannot enforce easily), so let's add
this missing dependency.

Fixes: 1a01695615f9 ("power: regulator: add pwm regulator")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Udit Kumar <u-kumar1@ti.com>
Reviewed-by: Anshul Dalal <anshuld@ti.com>
Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>