libata/IDE: remove combined mode quirk

Both old-IDE and libata should be able handle all controllers and
devices found using normal resource reservation methods.

This eliminates the awful, low-performing split-driver configuration
where old-IDE drove the PATA portion of a PCI device, in PIO-only mode,
and libata drove the SATA portion of the /same/ PCI device, in DMA mode.
Typically vendors would ship SATA hard drive / PATA optical
configuration, which would lend itself to slow (PIO-only) CD-ROM
performance.

For Intel users running in combined mode, it is now wholly dependent on
your driver choice (potentially link order, if you compile both drivers
in) whether old-IDE or libata will drive your hardware.

In either case, you will get full performance from both SATA and PATA
ports now, without having to pass a kernel command line parameter.

Signed-off-by: Jeff Garzik <jeff@garzik.org>