ARM: snapper9260: 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/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig
index 30c4e17..b660a5b 100644
--- a/arch/arm/mach-at91/Kconfig
+++ b/arch/arm/mach-at91/Kconfig
@@ -30,6 +30,9 @@
 config TARGET_SNAPPER9260
 	bool "Support snapper9260"
 	select CPU_ARM926EJS
+	select DM
+	select DM_SERIAL
+	select DM_GPIO
 
 config TARGET_AFEB9260
 	bool "Support afeb9260"