qemu-options: Add missing "sockets=2, maxcpus=2" to CLI "-smp 2"

qemu-options: Add missing "sockets=2, maxcpus=2" to CLI "-smp 2"

There is one numa config example in qemu-options.hx currently
using "-smp 2" and assuming that there will be 2 sockets and
2 cpus totally. However now the actual calculation logic of
missing sockets and cores is not immutable and is considered
liable to change. Although we will get maxcpus=2 finally based
on current parser, it's always stable to specify it explicitly.

So "-smp 2,sockets=2,maxcpus=2" will be optimal when we expect
multiple sockets and 2 cpus totally.

Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Message-Id: <20210928121134.21064-3-wangyanan55@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>