net/mlx5: poll cmd EQ in case of command timeout

Once driver detects a command interface command timeout, it warns the
user and returns timeout error to the caller. In such case, the entry of
the command is not evacuated (because only real event interrupt is allowed
to clear command interface entry). If the HW event interrupt
of this entry will never arrive, this entry will be left unused forever.
Command interface entries are limited and eventually we can end up without
the ability to post a new command.

In addition, if driver will not consume the EQE of the lost interrupt and
rearm the EQ, no new interrupts will arrive for other commands.

Add a resiliency mechanism for manually polling the command EQ in case of
a command timeout. In case resiliency mechanism will find non-handled EQE,
it will consume it, and the command interface will be fully functional
again. Once the resiliency flow finished, wait another 5 seconds for the
command interface to complete for this command entry.

Define mlx5_cmd_eq_recover() to manage the cmd EQ polling resiliency flow.
Add an async EQ spinlock to avoid races between resiliency flows and real
interrupts that might run simultaneously.

Fixes: e126ba97 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>