dm: remove redundant CONFIG_DM from driver/core/Makefile

As you see in driver/Makefile, Kbuild descends into the driver/core/
directory only when CONFIG_DM is enabled.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>

drivers/core/Makefile

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_DM)	+= device.o lists.o root.o uclass.o util.o
+obj-y	+= device.o lists.o root.o uclass.o util.o
 ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_OF_CONTROL) += simple-bus.o
 endif