MAINTAINERS: Update KVM/MIPS maintainers

James Hogan has become inactive for a long time and leaves KVM for MIPS
orphan. I'm working on KVM/Loongson and attempt to make it upstream both
in kernel and QEMU, while Aleksandar Markovic is already a maintainer of
QEMU/MIPS. We are both interested in QEMU/KVM/MIPS, and we have already
made some contributions in kernel and QEMU. If possible, we want to take
the KVM/MIPS maintainership.

Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>