scsi: megaraid_sas: Selectively apply stream detection based on IO type

Performance improvement:

Current driver calls stream detection unconditionally for all IOs.
Stream Detection logic is not required for most of the fast path IO. To
improve performance, avoid stream detection logic and do it only if
required.

Below are the cases where stream detection is required in driver:

1. All non-FastPath IOs (IOs going to FW)
2. Fast Path reads sent to ReadAhead capable VDs.

Signed-off-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>