tsnep: Add TSN endpoint Ethernet MAC driver

The TSN endpoint Ethernet MAC is a FPGA based network device for
real-time communication.

It is integrated as Ethernet controller with ethtool and PTP support.
For real-time communcation TC_SETUP_QDISC_TAPRIO is supported.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>