MAINTAINERS: Add myself as a reviewer of LoongArch virt machine

MAINTAINERS: Add myself as a reviewer of LoongArch virt machine

I would like to be informed on changes made to the LoongArch virt machine.

I'm fairly familiar with Loongson-3 series platform hardware and doing
firmwre (U-Boot) development as hobbyist on LoongArch virt platform,
so I believe I can give positive review input to changes on that machine.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20240627-ipi-fixes-v1-2-9b061dc28a3a@flygoat.com>
Signed-off-by: Song Gao <gaosong@loongson.cn>