redhat: Enable virtio-mem as tech-preview on x86-64

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2014484 Upstream-status: RHEL-only

Everything necesssary for tech-preview of virtio-mem in RHEL9 is included in QEMU v6.2. Let's enable it via the config option CONFIG_VIRTIO_MEM on x86-64.

Signed-off-by: David Hildenbrand david@redhat.com