ARM: stv0991: use "select" instead of default value in defconfig

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

arch/arm/Kconfig

@@ -235,6 +235,8 @@ config TARGET_SPEAR600
 config TARGET_STV0991
 	bool "Support stv0991"
 	select CPU_V7
+	select DM
+	select DM_SERIAL
 
 config TARGET_X600
 	bool "Support x600"

configs/stv0991_defconfig

@@ -2,5 +2,3 @@ CONFIG_SYS_EXTRA_OPTIONS="stv0991"
 CONFIG_ARM=y
 CONFIG_TARGET_STV0991=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000
-CONFIG_DM=y
-CONFIG_DM_SERIAL=y