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/xtfpga_defconfig b/configs/xtfpga_defconfig
index 78f8d63..431267f 100644
--- a/configs/xtfpga_defconfig
+++ b/configs/xtfpga_defconfig
@@ -3,6 +3,7 @@
 CONFIG_ENV_SIZE=0x20000
 CONFIG_ENV_SECT_SIZE=0x20000
 CONFIG_XTFPGA_KC705=y
+CONFIG_SYS_LOAD_ADDR=0x02000000
 CONFIG_SHOW_BOOT_PROGRESS=y
 CONFIG_BOOTDELAY=10
 CONFIG_AUTOBOOT_KEYED=y