power: regulator: Kconfig: add a dependency for POWER_SUPPORT for SPL

power/regulator will not be built if just CONFIG_SPL_DM_REGULATOR is
enabled. It needs CONFIG_SPL_POWER_SUPPORT to be enabled as well.

For example, if we just need a GPIO regulator in SPL:
CONFIG_DM_REGULATOR=y
CONFIG_SPL_DM_REGULATOR=y
CONFIG_DM_REGULATOR_GPIO=y
CONFIG_SPL_DM_REGULATOR_GPIO=y

Will not suffice, since the entire regulator build for SPL depends on
CONFIG_SPL_POWER_SUPPORT. Elaborate that information in the Kconfig
dependency.

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/power/regulator/Kconfig b/drivers/power/regulator/Kconfig
index d431102..fbbea18 100644
--- a/drivers/power/regulator/Kconfig
+++ b/drivers/power/regulator/Kconfig
@@ -18,7 +18,7 @@
 
 config SPL_DM_REGULATOR
 	bool "Enable regulators for SPL"
-	depends on DM_REGULATOR
+	depends on DM_REGULATOR && SPL_POWER_SUPPORT
 	---help---
 	Regulators are seldom needed in SPL. Even if they are accessed, some
 	code space can be saved by accessing the PMIC registers directly.