kconfig: armv8: move CONFIG_ARM64 to Kconfig

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/configs/ls2085a_simu_defconfig b/configs/ls2085a_simu_defconfig
index efa8e74..7563a75 100644
--- a/configs/ls2085a_simu_defconfig
+++ b/configs/ls2085a_simu_defconfig
@@ -1,3 +1,3 @@
-CONFIG_SYS_EXTRA_OPTIONS="ARM64,SIMU"
+CONFIG_SYS_EXTRA_OPTIONS="SIMU"
 CONFIG_ARM=y
 CONFIG_TARGET_LS2085A_SIMU=y