ARM: make ARCH_S3C24XX select USE_OF and clean-up boot/dts/Makefile

ARCH_S3C24XX is a very exceptional platform that some DT files in
arch/arm/boot/dts/, but does not select USE_OF.

All the other platforms with DT files correctly select USE_OF
directly or indirectly (Most of them are either ARCH_MULTIPLATFORM
or ARM_SINGLE_ARMV7M).

With ARCH_S3C24XX fixed, "ifeq ($(CONFIG_OF),y)" in DT Makefile
can be deleted.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/Kconfig

@@ -595,6 +595,7 @@ config ARCH_S3C24XX
 	select MULTI_IRQ_HANDLER
 	select NEED_MACH_IO_H
 	select SAMSUNG_ATAGS
+	select USE_OF
 	help
 	  Samsung S3C2410, S3C2412, S3C2413, S3C2416, S3C2440, S3C2442, S3C2443
 	  and S3C2450 SoCs based systems, such as the Simtec Electronics BAST

arch/arm/boot/dts/Makefile

 # SPDX-License-Identifier: GPL-2.0
-ifeq ($(CONFIG_OF),y)
-
 dtb-$(CONFIG_ARCH_ALPINE) += \
 	alpine-db.dtb
 dtb-$(CONFIG_MACH_ARTPEC6) += \
@@ -1104,4 +1102,3 @@ dtb-$(CONFIG_ARCH_ZX) += zx296702-ad1.dtb
 dtb-$(CONFIG_ARCH_ASPEED) += aspeed-bmc-opp-palmetto.dtb \
 	aspeed-bmc-opp-romulus.dtb \
 	aspeed-ast2500-evb.dtb
-endif