net/mlx5: add IB shared context alloc/free functions

net/mlx5: add IB shared context alloc/free functions

The Mellanox NICs support SR-IOV and have E-Switch feature.
When SR-IOV is set up in switchdev mode and E-Switch is enabled
we have so called VF representors in the system. All representors
belonging to the same E-Switch are created on the basis of the
single PCI function and with current implementation each representor
has its own dedicated Infiniband device and operates within its
own Infiniband context. It is proposed to provide representors
as ports of the single Infiniband device and operate on the
shared Infiniband context saving various resources. This patch
introduces appropriate structures.

Also the functions to allocate and free shared IB context for
multiport are added. The IB device context, Protection Domain,
device attributes, Infiniband names are going to be relocated
to the shared structure from the device private one.
mlx5_dev_spawn() is updated to support shared context.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Shahaf Shuler <shahafs@mellanox.com>