default-configs: Add TARGET_XML_FILES definition

loongarch64-linux-user has references to XML files so include them.

Fixes: d32688ec ("default-configs: Add loongarch linux-user support")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20231030054834.39145-6-akihiko.odaki@daynix.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
[AJB: remove base32 from list]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231106185112.2755262-2-alex.bennee@linaro.org>