arm: rmobile: kconfig: Remove '+S:' prefix from defconfig files

'+S' is unnecessary because boards of rmobile do not use SPL.
This removes from armadillo-800eva and kzm9g.
Signed-off-by: NNobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: NNobuhiro Iwamatsu <iwamatsu@nigauri.org>

configs/armadillo-800eva_defconfig

 CONFIG_ARM=y
-+S:CONFIG_RMOBILE=y
+CONFIG_RMOBILE=y
 CONFIG_TARGET_ARMADILLO_800EVA=y

configs/kzm9g_defconfig

 CONFIG_ARM=y
-+S:CONFIG_RMOBILE=y
+CONFIG_RMOBILE=y
 CONFIG_TARGET_KZM9G=y