Split the interrupt setup code into two parts: allocation and configuration.
Do the allocation before requesting the IOCFacts message.  This triggers
the LSI firmware to recognize the multiqueue should be enabled if available.
Multiqueue isn't used by the driver yet, but this also fixes a problem with
the cached IOCFacts not matching latter checks, leading to potential problems
with error recovery.

As a side-effect, fetch the driver tunables as early as possible.