NTB: Add ntb_msi_test support to ntb_test

When the ntb_msi_test module is available, the test code will trigger
each of the interrupts and ensure the corresponding occurrences files
gets incremented.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Allen Hubbe <allenbh@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>