libata: Strict checking for identify reporting

The ATA specifications require checks on certain flags before assuming
the validity of other data. Go through the methods and correct those
needing extra checks. Also note limits on ata_id_major_version with
respect to ATA-1 and ATA-2. Correct the 32bit PIO check.

Wants to sit in -mm for a bit in case of a screwup on my part that I
didn't hit on the test drives and also in case someone, somewhere has
a drive that gets it wrong.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>