ide: allow host drivers to specify IRQ flags

* Add ->irq_flags field to struct ide_port_info and struct ide_host.

* Update host drivers and IDE PCI code to use ->irq_flags field.

* Convert init_irq() and ide_intr() to use host->irq_flags.

This fixes handling of shared IRQs for non-PCI hosts
and removes ugly ifdeffery from core IDE code.

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