Convert CONFIG_SYS_LOAD_ADDR to Kconfig

Now that we have consistent usage, migrate this symbol to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Rick Chen <rick@andestech.com>
diff --git a/configs/imx8ulp_evk_defconfig b/configs/imx8ulp_evk_defconfig
index 2a97c6d..016cc70 100644
--- a/configs/imx8ulp_evk_defconfig
+++ b/configs/imx8ulp_evk_defconfig
@@ -17,6 +17,7 @@
 CONFIG_SPL_IMX_ROMAPI_LOADADDR=0x88000000
 CONFIG_SPL_LOAD_IMX_CONTAINER=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_LOAD_ADDR=0x80480000
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_BOOTDELAY=0