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/stv0991_defconfig b/configs/stv0991_defconfig
index 7fe5f99..d8008a8 100644
--- a/configs/stv0991_defconfig
+++ b/configs/stv0991_defconfig
@@ -10,6 +10,7 @@
 CONFIG_ENV_OFFSET=0x30000
 CONFIG_ENV_SECT_SIZE=0x10000
 CONFIG_DEFAULT_DEVICE_TREE="stv0991"
+CONFIG_SYS_LOAD_ADDR=0x0
 CONFIG_SYS_EXTRA_OPTIONS="STV0991"
 CONFIG_BOOTDELAY=3
 CONFIG_AUTOBOOT_KEYED=y