The return value from pci_enable_msi() can not always be trusted.  This patch
adds code to generate an interrupt after MSI has been enabled and tests
whether or not we can receive and process it.  If the tests fails, then fall
back to LSI.
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>