vhost-user: Remove acpi-specific memslot limit

vhost-user: Remove acpi-specific memslot limit

Let's just support 512 memslots on x86-64 and aarch64 as well. The maximum
number of ACPI slots (256) is no longer completely expressive ever since
we supported virtio-based memory devices. Further, we're completely
ignoring other memslots used outside of memory device context, such as
memslots used for boot memory.

Note that the vhost memslot limit in the kernel is usually configured to
be 509. With this change, we prepare vhost-user on the QEMU side to be
closer to that limit, to eventually support ~512 memslots in most vhost
implementations and have less "surprises" when cold/hotplugging vhost
devices while also consuming more memslots than we're currently used to
by memory devices (e.g., once virtio-mem starts using multiple memslots).

Note that most vhost-user implementations only support a small number of
memslots so far, which we can hopefully improve in the near future.

We'll leave the PPC special-case as is for now.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20230503184144.808478-1-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>