net/mlx5: Handle SF IRQ request in the absence of SF IRQ pool

In case the SF IRQ pool is not available due to setup limitations,
SF currently relies on the already allocated PF IRQs to fulfill
its IRQ vector requests.

However, with the dynamic EQ allocation introduced in the next patch,
it is possible that not all IRQs of PF will be allocated after the driver
is loaded. In such case, if a SF requests a completion IRQ without having
its own independent IRQ pool, SF will lack a PF IRQ to utilize.

To address this scenario, allocate an IRQ for the SF from the PF's IRQ pool
on demand. The new IRQ will be shared between the SF and it's PF.

Signed-off-by: Maher Sanalla <msanalla@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>