powerpc/85xx: Add eTSEC 2.0 support for P1020RDB boards

This patch adds support for eTSEC 2.0 as found in P1020.
The changes include introduction of the group nodes for
the etsec nodes.

Signed-off-by: Sandeep Gopalpet <sandeep.kumar@freescale.com>
Signed-off-by: Anton Vorontsov <avorontsov@mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>