libata: implement LPM support for port multipliers
Port multipliers can do DIPM on fan-out links fine. Implement support
for it. Tested w/ SIMG 57xx and marvell PMPs. Both the host and
fan-out links enter power save modes nicely.
SIMG 37xx and 47xx report link offline on SStatus causing EH to detach
the devices. Blacklisted.
Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>