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/nokia_rx51_defconfig b/configs/nokia_rx51_defconfig
index 981e6f9..7a16767 100644
--- a/configs/nokia_rx51_defconfig
+++ b/configs/nokia_rx51_defconfig
@@ -7,6 +7,7 @@
 CONFIG_OPTIMIZE_INLINING=y
 CONFIG_LTO=y
 # CONFIG_SYS_MALLOC_F is not set
+CONFIG_SYS_LOAD_ADDR=0x80000000
 # CONFIG_FIT is not set
 CONFIG_BOOTDELAY=30
 CONFIG_AUTOBOOT_KEYED=y