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/M5272C3_defconfig b/configs/M5272C3_defconfig
index 0a6360d..87b895c 100644
--- a/configs/M5272C3_defconfig
+++ b/configs/M5272C3_defconfig
@@ -4,6 +4,7 @@
 CONFIG_ENV_SECT_SIZE=0x2000
 CONFIG_DEFAULT_DEVICE_TREE="M5272C3"
 CONFIG_TARGET_M5272C3=y
+CONFIG_SYS_LOAD_ADDR=0x20000
 CONFIG_BOOTDELAY=5
 # CONFIG_DISPLAY_BOARDINFO is not set
 # CONFIG_CMDLINE_EDITING is not set