net/mlx5: Expose SFs IRQs

Expose the sysfs files for the IRQs that the mlx5 PCI SFs are using.
These entries are similar to PCI PFs and VFs in 'msi_irqs' directory.

Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

---
v8-v9:
- add Przemek RB
v6->v7:
- remove not needed changes to mlx5 sfnum SF sysfs
v5->v6:
- fail IRQ creation in case auxiliary_device_sysfs_irq_add() failed
  (Parav and Przemek)
v2->v3:
- fix mlx5 sfnum SF sysfs