Add support for NXP/Freescale etsec2 ethernet controller

Adding the compatible property check isn't enough. Device trees for eTSEC2
devices are missing a 'reg' property on the eTSEC node itself, relegating it to
the queue group child nodes.

Still left to do: add Multigroup mode support (see QorIQ reference manuals s for
SoCs with eTSEC2).

MFC after: 2 weeks
Relnotes: Yes