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/helios4_defconfig b/configs/helios4_defconfig
index 4e59360..c3ea2c8 100644
--- a/configs/helios4_defconfig
+++ b/configs/helios4_defconfig
@@ -19,6 +19,7 @@
 CONFIG_DEBUG_UART=y
 CONFIG_AHCI=y
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_SYS_LOAD_ADDR=0x800000
 CONFIG_BOOTDELAY=3
 CONFIG_USE_PREBOOT=y
 CONFIG_SYS_CONSOLE_INFO_QUIET=y