openrisc: add arch/openrisc/Kbuild

Describe the subdirectories under arch/openrisc/ in arch/openrisc/Kbuild
so you can use the standard obj-y syntax.

I removed the CONFIG_OPENRISC_BUILTIN_DTB conditional because it is
already controlled by arch/openrisc/boot/dts/Makefile.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Stafford Horne <shorne@gmail.com>

arch/openrisc/Kbuild

+# SPDX-License-Identifier: GPL-2.0
+obj-y += lib/ kernel/ mm/
+obj-y += boot/dts/

arch/openrisc/Makefile

@@ -42,18 +42,9 @@ endif
 
 head-y 		:= arch/openrisc/kernel/head.o
 
-core-y		+= arch/openrisc/lib/ \
-		   arch/openrisc/kernel/ \
-		   arch/openrisc/mm/
+core-y		+= arch/openrisc/
 libs-y		+= $(LIBGCC)
 
-ifneq '$(CONFIG_OPENRISC_BUILTIN_DTB)' '""'
-BUILTIN_DTB := y
-else
-BUILTIN_DTB := n
-endif
-core-$(BUILTIN_DTB) += arch/openrisc/boot/dts/
-
 PHONY += vmlinux.bin
 
 vmlinux.bin: vmlinux