The description about virt machine type is removed by mistake, add
new description here. Here is output result with command
"./qemu-system-loongarch64 -M help"
Supported machines are:
none empty machine
virt QEMU LoongArch Virtual Machine (default)
x-remote Experimental remote machine
Without the patch, it shows as follows:
Supported machines are:
none empty machine
virt (null) (default)
x-remote Experimental remote machine
Fixes: ef2f11454c(hw/loongarch/virt: Replace Loongson IPI with LoongArch IPI)