doc: announce ABI change for device parameters

doc: announce ABI change for device parameters

The PCI and virtual bus are planned to be moved to the generic
drivers/bus directory in v17.08. For this change to be possible, the EAL
must be made completely independent.

The rte_devargs structure currently holds device representation internal
to those two busses. It must be made generic before this work can be
completed.

Instead of using either a driver name for a vdev or a PCI address for a
PCI device, a devargs structure will have to be able to describe any
possible device on all busses, without introducing dependencies on
any bus-specific device representation. This will break the ABI for this
structure.

Additionally, an evolution will occur regarding the device parsing
from the command-line. A user must be able to set which bus will handle
which device, and this setting is integral to the definition of a
device.

The format has not yet been formally defined, but a proposition will
follow soon for a new command line parameter format for all devices.

Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: David Marchand <david.marchand@6wind.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>