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/xenguest_arm64_defconfig b/configs/xenguest_arm64_defconfig
index e170761..296d175 100644
--- a/configs/xenguest_arm64_defconfig
+++ b/configs/xenguest_arm64_defconfig
@@ -4,6 +4,7 @@
 CONFIG_SYS_TEXT_BASE=0x40080000
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_IDENT_STRING=" xenguest"
+CONFIG_SYS_LOAD_ADDR=0x40000000
 CONFIG_BOOTDELAY=10
 CONFIG_SYS_PROMPT="xenguest# "
 # CONFIG_CMD_BDI is not set