ARM: rmobile: salvator-x: Update defconfig

This moves some config from config files.
Signed-off-by: NNobuhiro Iwamatsu <iwamatsu@nigauri.org>

configs/salvator-x_defconfig

 CONFIG_ARM=y
+CONFIG_ARCH_RMOBILE=y
+CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_RCAR_GEN3=y
 CONFIG_TARGET_SALVATOR_X=y
-CONFIG_SPL=y
+CONFIG_BOOTSTAGE_USER_COUNT=0x20
+CONFIG_BOOTSTAGE_STASH_ADDR=0x0
+CONFIG_BOOTSTAGE_STASH_SIZE=0x4096
+CONFIG_CMD_BOOTZ=y
+# CONFIG_CMD_IMI is not set
+# CONFIG_CMD_IMLS is not set
+# CONFIG_CMD_XIMG is not set