eal: add bus pointer in device structure

eal: add bus pointer in device structure

When a device is added with a devargs (hotplug or whitelist),
the bus pointer can be retrieved via its devargs.
But there is no such devargs.bus in case of standard scan.

A pointer to the rte_bus handle is added to rte_device.
When a device is allocated (during a scan),
the pointer to its bus is assigned.

It will make possible to remove a rte_device,
using the function pointer from its bus.

The function rte_bus_find_by_device() becomes useless,
and may be removed later.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>