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/rock960-rk3399_defconfig b/configs/rock960-rk3399_defconfig
index 0233e0e..fee46c4 100644
--- a/configs/rock960-rk3399_defconfig
+++ b/configs/rock960-rk3399_defconfig
@@ -8,6 +8,7 @@
 CONFIG_DEBUG_UART_BASE=0xFF1A0000
 CONFIG_DEBUG_UART_CLOCK=24000000
 CONFIG_DEBUG_UART=y
+CONFIG_SYS_LOAD_ADDR=0x800800
 CONFIG_USE_PREBOOT=y
 CONFIG_DEFAULT_FDT_FILE="rockchip/rk3399-rock960.dtb"
 CONFIG_DISPLAY_BOARDINFO_LATE=y