net/mlx5: SD, Implement devcom communication and primary election

Use devcom to communicate between the different devices. Add a new
devcom component type for this.

Each device registers itself to the devcom component <SD, group ID>.
Once all devices of a component are registered, the component becomes
ready, and a primary device is elected.

In principle, any of the devices can act as a primary, they are all
capable, and a random election would've worked. However, we aim to
achieve predictability and consistency, hence each group always choses
the same device, with the lowest PCI BUS number, as primary.

Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>