net: atm: remove the ambassador driver

The driver for ATM Ambassador devices spews build warnings on
microblaze. The virt_to_bus() calls discard the volatile keyword.
The right thing to do would be to migrate this driver to a modern
DMA API but it seems unlikely anyone is actually using it.
There had been no fixes or functional changes here since
the git era begun.

In fact it sounds like the FW loading was broken from 2008
'til 2012 - see commit fcdc90b0 ("atm: forever loop loading
ambassador firmware").

Let's remove this driver, there isn't much changing in the APIs,
if users come forward we can apologize and revert.

Link: https://lore.kernel.org/all/20220321144013.440d7fc0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com/


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>