PATA PIIX uses reset signature + TF r/w test for device presence
detection, which doesn't always work.  It sometimes reports phantom
device which results in IDENTIFY timeouts.

SATA PIIX uses some combination of PCS + reset signature + TF r/w test
for device presence detection.  No combination satifies all and for
some controllers, there doesn't seem to be any combination which
works reliably.

This patch makes both PATA and SATA piix's use reset signature + TF
r/w + polling IDENTIFY for device detection.  This is what the old
libata (before irq-pio and new EH) did and what IDE does.

This patch also removes now obsolete PIIX_FLAG_IGNORE_PCS, force_pcs
and related code.
Signed-off-by: Jeff Garzik <jeff@garzik.org>