PCI: Add #defines for Hypertransport MSI fields

Add a few #defines for grabbing and working with the address fields
in a HT_CAPTYPE_MSI_MAPPING capability. All from the HT spec v3.00.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>