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/ds414_defconfig b/configs/ds414_defconfig
index f10f149..70a1bd1 100644
--- a/configs/ds414_defconfig
+++ b/configs/ds414_defconfig
@@ -18,6 +18,7 @@
 CONFIG_DEBUG_UART_BASE=0xd0012000
 CONFIG_DEBUG_UART_CLOCK=250000000
 CONFIG_DEBUG_UART=y
+CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 ip=off initrd=0x8000040,8M root=/dev/md0 rw syno_hw_version=DS414r1 ihd_num=4 netif_num=2 flash_size=8 SataLedSpecial=1 HddHotplug=1"