igc: Add support for LEDs on i225/i226

Add support for LEDs on i225/i226. The LEDs can be controlled via sysfs
from user space using the netdev trigger. The LEDs are named as
igc-<bus><device>-<led> to be easily identified.

Offloading link speed and activity are supported. Other modes are simulated
in software by using on/off. Tested on Intel i225.

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://lore.kernel.org/r/20240213184138.1483968-1-anthony.l.nguyen@intel.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>