libata: set NODEV_HINT for 0x7f status

Asus Pundit-R with atiixp controller has the second port missing and,
very unusually, its status is stuck at 0x7f and all others at 0.  This
meanst that it fails TF access test but gets detected as a disk due to
classification code check and then evades polling IDENTIFY presence
detection thanks to the missing BSY in the status value causing
excessive delays during boot.

This patch makes libata-sff HSM set NODEV_HINT if the status is 0x7f
to make polling IDENTIFY presence detection work for these machines.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>