[PATCH] libata: ACPI and _GTF support

_GTF is an acpi method that is used to reinitialize the drive.  It returns
a task file containing ata commands that are sent back to the drive to restore
it to boot up defaults.

Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
(cherry picked from 9c69cab24b51a89664f4c0dfaf8a436d32117624 commit)