pmdomain: rockchip: add regulator dependency

When CONFIG_REGULATOR is disabled, this pmdomain driver fails to build:

drivers/pmdomain/rockchip/pm-domains.c:653:30: error: implicit declaration of function 'devm_of_regulator_get'; did you mean 'devm_regulator_get'? [-Wimplicit-function-declaration]
  653 |                 pd->supply = devm_of_regulator_get(pmu->dev, pd->node, "domain");
      |                              ^~~~~~~~~~~~~~~~~~~~~
      |                              devm_regulator_get
drivers/pmdomain/rockchip/pm-domains.c:653:28: error: assignment to 'struct regulator *' from 'int' makes pointer from integer without a cast [-Wint-conversion]
  653 |                 pd->supply = devm_of_regulator_get(pmu->dev, pd->node, "domain");
      |                            ^

Add a Kconfig dependency.

Fixes: db6df2e ("pmdomain: rockchip: add regulator support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20250304142803.689201-1-arnd@kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: arndb

drivers/pmdomain/rockchip/Kconfig

@@ -5,6 +5,7 @@ config ROCKCHIP_PM_DOMAINS
 	bool "Rockchip generic power domain"
 	depends on PM
 	depends on HAVE_ARM_SMCCC_DISCOVERY
+	depends on REGULATOR
 	select PM_GENERIC_DOMAINS
 	help
 	  Say y here to enable power domain support.