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/malta_defconfig b/configs/malta_defconfig
index 0e9babd..03ad70a 100644
--- a/configs/malta_defconfig
+++ b/configs/malta_defconfig
@@ -4,6 +4,7 @@
 CONFIG_ENV_SECT_SIZE=0x20000
 CONFIG_DEFAULT_DEVICE_TREE="mti,malta"
 CONFIG_TARGET_MALTA=y
+CONFIG_SYS_LOAD_ADDR=0x81000000
 # CONFIG_AUTOBOOT is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_MISC_INIT_R=y