am335x_evm: Convert NOR_BOOT to Kconfig

Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/configs/am335x_evm_norboot_defconfig b/configs/am335x_evm_norboot_defconfig
index d2d3ba2..47ff6cd 100644
--- a/configs/am335x_evm_norboot_defconfig
+++ b/configs/am335x_evm_norboot_defconfig
@@ -1,5 +1,5 @@
-CONFIG_SYS_EXTRA_OPTIONS="NOR_BOOT"
 CONFIG_CONS_INDEX=1
 CONFIG_ARM=y
 CONFIG_TARGET_AM335X_EVM=y
 CONFIG_NOR=y
+CONFIG_NOR_BOOT=y