hw/rdma: VMW_PVRDMA should depend on VMXNET3_PCI

hw/rdma: VMW_PVRDMA should depend on VMXNET3_PCI

The "pvrdma" device is only usable in conjunction with the "vmxnet3"
NIC - see the check for TYPE_VMXNET3 in pvrdma_realize().

By adding this dependency, the amount of total files that have to
be compiled for a configuration with all targets decreases by 64
files (!), since the rdma code is marked as target specific and thus
got recompiled for all targets that enable PCI so far.

Message-Id: <20230419111337.651673-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>