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/socfpga_agilex_vab_defconfig b/configs/socfpga_agilex_vab_defconfig
index c802827..11cf232 100644
--- a/configs/socfpga_agilex_vab_defconfig
+++ b/configs/socfpga_agilex_vab_defconfig
@@ -13,6 +13,7 @@
 CONFIG_TARGET_SOCFPGA_AGILEX_SOCDK=y
 CONFIG_IDENT_STRING="socfpga_agilex"
 CONFIG_SPL_FS_FAT=y
+CONFIG_SYS_LOAD_ADDR=0x02000000
 CONFIG_FIT=y
 CONFIG_SPL_FIT_SIGNATURE=y
 CONFIG_SPL_LOAD_FIT=y