common/mlx5: add bus-agnostic layer

common/mlx5: add bus-agnostic layer

To support auxiliary bus, introduces common device driver and callbacks,
supposed to replace mlx5 common PCI bus driver.

Mlx5 class drivers, i.e. eth, vDPA, regex and compress normally consumes
single Verbs device context to probe a device. The Verbs device comes
from PCI address if the device is PCI bus device, from Auxiliary sysfs
if the device is auxiliary bus device. Currently only PCI bus is
supported.

Common device driver is a middle layer between mlx5 class drivers and
bus, resolve and abstract bus info to Verbs device for class drivers.
Both PCI bus driver and Auxiliary bus driver can utilize the common
driver layer to cast bus operations to mlx5 class drivers.

Legacy mlx5 common PCI bus driver still being used by mlx5 eth, vDPA,
regex and compress PMD, will be removed once all PMD drivers
migrate to new common driver.

Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>