MAINTAINERS: add myself as the maintainer for LoongArch VirtMachine

MAINTAINERS: add myself as the maintainer for LoongArch VirtMachine

Song Gao is will be sick leave for a long time, I apply for maintainer
for LoongArch Virt Machine during this period, LoongArch TCG keeps unchanged
since I am not familiar with it. The maintainer duty will transfer to him
after he comes back to work.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Acked-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20241112073714.1953481-1-maobibo@loongson.cn>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>