[coreboot] filo: Skip native ATA controllers in find_ide_controller_compat()

[Peter Stuge]

Patch not signed off since I haven't tested this at all.

I would appreciate test results from using this patch on boards which
have both SATA controller(s) and one or more PATA controllers in
compatibility (AKA legacy) mode.

Previously it was not possible to boot from a drive on a PATA
controller in compat mode when there were PCI devices in native
mode (SATA always are) on lower devfn numbers. Native mode devices
were basically still assumed to use the legacy IO ports in the code
looking up IO ports for compat devices.

Please set DEBUG_IDE=1 in Config and send output to me or the list.

Thanks!

//Peter