net/mlx5: Add Vendor Specific Capability access gateway

The Vendor Specific Capability (VSC) is used to activate a gateway
interfacing with the device. The gateway is used to read or write
device configurations, which are organized in different domains (spaces).
A configuration access may result in multiple actions, reads, writes.

Example usages are accessing the Crspace domain to read the crspace or
locking a device semaphore using the Semaphore domain.

The configuration access use pci_cfg_access to prevent parallel access to
the VSC space by the driver and userspace calls.

Signed-off-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Feras Daoud <ferasda@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>