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/highbank_defconfig b/configs/highbank_defconfig
index a6aed67..9eef601 100644
--- a/configs/highbank_defconfig
+++ b/configs/highbank_defconfig
@@ -8,6 +8,7 @@
 CONFIG_SYS_BOOTCOUNT_ADDR=0xfff3cf0c
 CONFIG_SYS_BOOTCOUNT_SINGLEWORD=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_FIT=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_AUTOBOOT_KEYED=y