igb: Fix not clearing TimeSync interrupts for 82580

igb: Fix not clearing TimeSync interrupts for 82580

82580 NICs have a hardware bug that makes it
necessary to write into the TSICR (TimeSync Interrupt Cause) register
to clear it:
https://lore.kernel.org/all/CDCB8BE0.1EC2C%25matthew.vick@intel.com/

Add a conditional so only for 82580 we write into the TSICR register,
so we don't risk losing events for other models.

Without this change, when running ptp4l with an Intel 82580 card,
I get the following output:

> timed out while polling for tx timestamp increasing tx_timestamp_timeout or
> increasing kworker priority may correct this issue, but a driver bug likely
> causes it

This goes away with this change.

This (partially) reverts commit ee14cc9ea19b ("igb: Fix missing time sync events").

Fixes: ee14cc9ea19b ("igb: Fix missing time sync events")
Closes: https://lore.kernel.org/intel-wired-lan/CAN0jFd1kO0MMtOh8N2Ztxn6f7vvDKp2h507sMryobkBKe=xk=w@mail.gmail.com/
Tested-by: Daiwei Li <daiweili@google.com>
Suggested-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Daiwei Li <daiweili@google.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>