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.