dm: Make regmap and syscon optional

Not all boards use garbage collection in their link step, so we should avoid
adding options that rely on this for prevention of code bloat. Add separate
Kconfig options for syscon and regmap uclasses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/Makefile b/drivers/core/Makefile
index 5c2ead8..ce3027a 100644
--- a/drivers/core/Makefile
+++ b/drivers/core/Makefile
@@ -10,5 +10,5 @@
 endif
 obj-$(CONFIG_DM_DEVICE_REMOVE)	+= device-remove.o
 obj-$(CONFIG_DM)	+= dump.o
-obj-$(CONFIG_OF_CONTROL)	+= regmap.o
-obj-$(CONFIG_OF_CONTROL)	+= syscon-uclass.o
+obj-$(CONFIG_REGMAP)	+= regmap.o
+obj-$(CONFIG_SYSCON)	+= syscon-uclass.o