ARM: cm_fx6: use "select" instead of default value in defconfig

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index af2d4f4..3702bb0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -630,6 +630,9 @@
 	bool "Support cm_fx6"
 	select CPU_V7
 	select SUPPORT_SPL
+	select DM
+	select DM_SERIAL
+	select DM_GPIO
 
 config TARGET_SOCFPGA_ARRIA5
 	bool "Support socfpga_arria5"