hw/rdma: Deprecate the pvrdma device and the rdma subsystem

hw/rdma: Deprecate the pvrdma device and the rdma subsystem

This subsystem is said to be in a bad shape (see e.g. [1], [2]
and [3]), and nobody seems to feel responsible to pick up patches
for this and send them via a pull request. For example there is
a patch for a CVE-worthy bug posted more than half a year ago [4]
which has never been merged. Thus let's mark it as deprecated and
finally remove it unless somebody steps up and improves the code
quality and adds proper regression tests.

[1] https://lore.kernel.org/qemu-devel/20230918144206.560120-1-armbru@redhat.com/
[2] https://lore.kernel.org/qemu-devel/ZQnojJOqoFu73995@redhat.com/
[3] https://lore.kernel.org/qemu-devel/1054981c-e8ae-c676-3b04-eeb030e11f65@tls.msk.ru/
[4] https://lore.kernel.org/qemu-devel/20230301142926.18686-1-yuval.shaia.ml@gmail.com/

Message-ID: <20230927133019.228495-1-thuth@redhat.com>
Acked-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>