sata_mv add temporary 3 second init delay for SiliconImage PMs

sata_mv does not yet fully support hotplug (coming soon, though).
This means that the driver may not find a Silicon Image port-multiplier
when first loaded, because those devices take in exceess of 3 seconds
to sync up the SATA PHY (most devices do this in mere microseconds).

So, as a short-term interim measure, here we insert a 3-second pause
on initial driver load, once per controller board (not once per port!),
to allow the Silicon Image port-multipliers to be detected later.

This will be removed again (soon!) once hotplug is fully implemented/working.

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>