ipr: differentiate pci-x and pci-e based adapters

MSI has only been tested on and known to work with PCI-E based adapters.  This
patch adds a field to struct ipr_chip_t to indicate which type of interrupt to
use based on what is known about the chip.

Signed-off-by: Wayne Boyer <wayneb@linux.vnet.ibm.com>
Acked-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>