macb: Basic suspend/resume support

This implements suspend and resume callbacks for the macb driver. We may
have to do some more to gracefully shut the MAC down, but this at least
prevents the macb from waking the system when hooked up to a busy
network.

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Patrice Vilchez <patrice.vilchez@rfo.atmel.com>
Cc: Nicolas FERRE <nicolas.ferre@rfo.atmel.com>