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/dockstar_defconfig b/configs/dockstar_defconfig
index 8d43609..405a32a 100644
--- a/configs/dockstar_defconfig
+++ b/configs/dockstar_defconfig
@@ -10,6 +10,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="kirkwood-dockstar"
 CONFIG_IDENT_STRING="\nSeagate FreeAgent DockStar"
 # CONFIG_SYS_MALLOC_F is not set
+CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_PREBOOT=y
 # CONFIG_DISPLAY_BOARDINFO is not set