It seems that on some nVidia controllers using AltStatus register
can be unreliable so default to Status register if the PCI device
is in Compatibility Mode.  In order to achieve this:

* Add ide_pci_is_in_compatibility_mode() inline helper to <linux/ide.h>.

* Add IDE_HFLAG_BROKEN_ALTSTATUS host flag and set it in amd74xx host
  driver for nVidia controllers in Compatibility Mode.

* Teach actual_try_to_identify() and drive_is_ready() about the new flag.

This fixes the regression caused by removal of CONFIG_IDEPCI_SHARE_IRQ
config option in 2.6.25 and using AltStatus register unconditionally when
available (kernel.org bugs #11659 and #10216).

[ Moreover for CONFIG_IDEPCI_SHARE_IRQ=y (which is what most people
  and distributions use) it never worked correctly. ]

Thanks to Remy LABENE and Lars Winterfeld for help with debugging the problem.

More info at:
http://bugzilla.kernel.org/show_bug.cgi?id=11659
http://bugzilla.kernel.org/show_bug.cgi?id=10216



Reported-by: Remy LABENE <remy.labene@free.fr>
Tested-by: Remy LABENE <remy.labene@free.fr>
Tested-by: Lars Winterfeld <lars.winterfeld@tu-ilmenau.de>
Acked-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>