Fall back to INTR_MPSAFE if INTR_FAST registration fails.
Fall back to INTR_MPSAFE if INTR_FAST registration fails.

PR:	kern/62276

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase