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/rock_defconfig b/configs/rock_defconfig
index 9122173..96bc4ee 100644
--- a/configs/rock_defconfig
+++ b/configs/rock_defconfig
@@ -14,6 +14,7 @@
 CONFIG_DEBUG_UART_BASE=0x20064000
 CONFIG_DEBUG_UART_CLOCK=24000000
 CONFIG_DEBUG_UART=y
+CONFIG_SYS_LOAD_ADDR=0x60800800
 CONFIG_USE_PREBOOT=y
 CONFIG_DEFAULT_FDT_FILE="rk3188-radxarock.dtb"
 # CONFIG_DISPLAY_CPUINFO is not set