Currently, ahci supports only msi and intx. To also support msix the
handling of the irq number need to be changed. The irq number for msix
devices is taken from msi_list instead of pci_dev. Thus, the irq
number of a device needs to be stored in struct ahci_host_priv now.
This allows the host controller to be activated in a generic way.

This change is only intended for ahci drivers. For that reason the irq
number is stored in struct ahci_host_priv used only by ahci drivers.
Thus, the ABI changes only for ahci_host_activate(), but existing ata
drivers (about 50) are unaffected and keep unchanged. All users of
ahci_host_activate() have been updated.

While touching drivers/ata/libahci.c, doing a small code cleanup in
ahci_port_start().
Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Tejun Heo <tj@kernel.org>