arm: mvebu: turris_omnia: Enable immutable debug settings in DDR3 training by default

Save 10 KiB in Turris Omnia's SPL binary by enabling immutable debug
settings for DDR3 training code.

Signed-off-by: Marek BehĂșn <kabel@kernel.org>
diff --git a/configs/turris_omnia_defconfig b/configs/turris_omnia_defconfig
index d569978..938ad88 100644
--- a/configs/turris_omnia_defconfig
+++ b/configs/turris_omnia_defconfig
@@ -10,6 +10,7 @@
 CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=y
 CONFIG_CUSTOM_SYS_INIT_SP_ADDR=0xff0000
 CONFIG_TARGET_TURRIS_OMNIA=y
+CONFIG_DDR_IMMUTABLE_DEBUG_SETTINGS=y
 CONFIG_DDR_RESET_ON_TRAINING_FAILURE=y
 CONFIG_MVEBU_EFUSE_VHV_GPIO="mcu_56"
 CONFIG_MVEBU_EFUSE_VHV_GPIO_ACTIVE_LOW=y