IB/ipath: Remove dependency on PCI_MSI || HT_IRQ

Before IBA7220 support was added, the ipath driver didn't support any
hardware unless PCI_MSI and/or HT_IRQ was enabled.  However, the
IBA7220 can generate INTx interrupts, so it makes sense to allow the
driver to be build even if PCI_MSI=n and HT_IRQ=n.

Signed-off-by: Roland Dreier <rolandd@cisco.com>