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/db-88f6720_defconfig b/configs/db-88f6720_defconfig
index 4ac2109..d05344d 100644
--- a/configs/db-88f6720_defconfig
+++ b/configs/db-88f6720_defconfig
@@ -18,6 +18,7 @@
 CONFIG_DEBUG_UART_CLOCK=250000000
 CONFIG_DEBUG_UART=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_PREBOOT=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y