buf_info structures in RX & TX queues are private driver data that
do not need to be visible to the device.  Although there is physical
address and length in the queue descriptor that points to these
structures, their layout is not standardized, and device never looks
at them.

So lets allocate these structures in non-DMA-able memory, and fill
physical address as all-ones and length as zero in the queue
descriptor.

That should alleviate worries brought by Martin Radev in
https://lists.osuosl.org/pipermail/intel-wired-lan/Week-of-Mon-20210104/022829.html
that malicious vmxnet3 device could subvert SVM/TDX guarantees.
Signed-off-by: Petr Vandrovec <petr@vmware.com>
Signed-off-by: Ronak Doshi <doshir@vmware.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>