gianfar: Remove legacy PM callbacks

These callbacks were needed because dev_pm_ops support for OF
platform devices was in the powerpc tree, and the patch that
added dev_pm_ops for gianfar driver was in the netdev tree. Now
that netdev and powerpc trees have merged into Linus' tree, we
can remove the legacy hooks.

Signed-off-by: Anton Vorontsov <avorontsov@mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>