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/zmx25_defconfig b/configs/zmx25_defconfig
index 2afe429..78277ce 100644
--- a/configs/zmx25_defconfig
+++ b/configs/zmx25_defconfig
@@ -5,6 +5,7 @@
 CONFIG_ENV_SIZE=0x20000
 CONFIG_ENV_SECT_SIZE=0x20000
 CONFIG_TARGET_ZMX25=y
+CONFIG_SYS_LOAD_ADDR=0x80000000
 CONFIG_BOOTDELAY=5
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="boot in %d s\n"