dm: power: Allow use of regulators in SPL

This functionality may be useful for setting up regulators early during
boot.

Signed-off-by: Simon Glass <sjg@chromium.org>

scripts/Makefile.spl

@@ -67,6 +67,7 @@ libs-y += fs/
 libs-$(CONFIG_SPL_LED_SUPPORT) += drivers/led/
 libs-$(CONFIG_SPL_LIBGENERIC_SUPPORT) += lib/
 libs-$(CONFIG_SPL_POWER_SUPPORT) += drivers/power/ drivers/power/pmic/
+libs-$(CONFIG_SPL_POWER_SUPPORT) += drivers/power/regulator/
 libs-$(CONFIG_SPL_MTD_SUPPORT) += drivers/mtd/
 libs-$(CONFIG_SPL_NAND_SUPPORT) += drivers/mtd/nand/
 libs-$(CONFIG_SPL_DRIVERS_MISC_SUPPORT) += drivers/misc/