dm: power: Allow regulators to be omitted from SPL

For some boards the pmic interface is useful but the regulator interface
(which comes with it) is too large. Allow them to be separated such that
SPL can decide which it needs.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/power/regulator/Makefile b/drivers/power/regulator/Makefile
index 0d18c2b..1590d85 100644
--- a/drivers/power/regulator/Makefile
+++ b/drivers/power/regulator/Makefile
@@ -5,11 +5,11 @@
 # SPDX-License-Identifier:     GPL-2.0+
 #
 
-obj-$(CONFIG_DM_REGULATOR) += regulator-uclass.o
+obj-$(CONFIG_$(SPL_)DM_REGULATOR) += regulator-uclass.o
 obj-$(CONFIG_REGULATOR_ACT8846) += act8846.o
 obj-$(CONFIG_DM_REGULATOR_MAX77686) += max77686.o
 obj-$(CONFIG_DM_REGULATOR_PFUZE100) += pfuze100.o
-obj-$(CONFIG_DM_REGULATOR_FIXED) += fixed.o
+obj-$(CONFIG_$(SPL_)DM_REGULATOR_FIXED) += fixed.o
 obj-$(CONFIG_REGULATOR_RK808) += rk808.o
 obj-$(CONFIG_REGULATOR_S5M8767) += s5m8767.o
 obj-$(CONFIG_DM_REGULATOR_SANDBOX) += sandbox.o