SCSI: Allow MPT Fusion SAS 3.0 driver to be built into the kernel

Right now the Makefile for the mpt3sas driver does not even allow the
driver to be built into the kernel.  So fix that up, as there doesn't
seem to be any obvious reason why this shouldn't be done.

Cc: Nagalakshmi Nandigama <Nagalakshmi.Nandigama@lsi.com>
Cc: Sreekanth Reddy <Sreekanth.Reddy@lsi.com>
Cc: support@lsi.com
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>