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/ap152_defconfig b/configs/ap152_defconfig
index 0f7a817..9f02c50 100644
--- a/configs/ap152_defconfig
+++ b/configs/ap152_defconfig
@@ -13,6 +13,7 @@
 CONFIG_ARCH_ATH79=y
 CONFIG_TARGET_AP152=y
 CONFIG_DEBUG_UART=y
+CONFIG_SYS_LOAD_ADDR=0x81000000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 root=/dev/mtdblock2 rootfstype=squashfs"