drivers: ethernet: enc28j60: Added carrier status update functionality

Expanded the enc28j60 driver to update its carrier status
whenever the Ethernet cable is plugged in or out. I used the
enc424j600 driver as reference, as this driver already
included this functionality. The driver will now take
the interface offline whenever the cable is not plugged in
and stop sending packets. The respective events are also
generated for use in the application. I tested it locally
on my nRF52840 based gateway board using the enc28j60 network
chip. Everything worked as expected.

Signed-off-by: Paul Jans <paul.jans.1999@hotmail.com>

Fixes #51214