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/amcore_defconfig b/configs/amcore_defconfig
index a17cc21..8153fda 100644
--- a/configs/amcore_defconfig
+++ b/configs/amcore_defconfig
@@ -5,6 +5,7 @@
 CONFIG_ENV_SECT_SIZE=0x1000
 CONFIG_DEFAULT_DEVICE_TREE="amcore"
 CONFIG_TARGET_AMCORE=y
+CONFIG_SYS_LOAD_ADDR=0x20000
 CONFIG_BOOTDELAY=1
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 # CONFIG_DISPLAY_BOARDINFO is not set