Add IDE_HFLAG_FORCE_LEGACY_IRQS host flag to tell ide_pci_setup_ports()
to always set hwif->irq to legacy IRQ 14/15 and convert generic IDE PCI
and via82cxxx host drivers to use it.

While at it:

* Add IDE_HFLAGS_UMC define (generic IDE PCI host driver).

* Remove no longer needed init_hwif_generic() (generic IDE PCI host driver).

* Set d->udma_mask instead of hwif->ultra_mask (via82cxxx host driver).

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>