1. Rename 'loongson3.c' to 'virt.c' and change the meson.build file.
2. Rename 'loongson3.rst' to 'virt.rst'.

Signed-off-by: Xiaojuan Yang <yangxiaojuan@loongson.cn>
Message-Id: <20220729073018.27037-2-yangxiaojuan@loongson.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>