hw/loongarch/virt: Add separate file for fdt building

Similiar with virt-acpi-build.c, file virt-fdt-build.c is added here.
And move functions relative with fdt table building to the file.

It is only code movement and there is no function change.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
4 files changed