mpt3sas: Add dummy Kconfig option for backwards compatibility

The mpt2sas driver was recently folded into mpt3sas to reduce code
duplication.

To avoid problems for people that only have CONFIG_SCSI_MPT2SAS in their
.config we introduce a dummy option that will select MPT3SAS if MPT2SAS
was previously enabled.

This is a temporary measure and we will deprecate this config option in
4.6.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Acked-by: James Bottomley <James.Bottomley@hansenpartnership.com>
CC: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpt3sas/Kconfig

@@ -71,3 +71,11 @@ config SCSI_MPT3SAS_MAX_SGE
 	MAX_PHYS_SEGMENTS in most kernels.  However in SuSE kernels this
 	can be 256. However, it may decreased down to 16.  Decreasing this
 	parameter will reduce memory requirements on a per controller instance.
+
+config SCSI_MPT2SAS
+	tristate "Legacy MPT2SAS config option"
+	default n
+	select SCSI_MPT3SAS
+	---help---
+	Dummy config option for backwards compatiblity: configure the MPT3SAS
+	driver instead.