Use all data disks for sequential read operations.

Testing discovered inconsistent performance on RAID 10 volumes when
performing 256K sequential reads. The driver was only using a single
tracker to determine which physical drive to send a request to for AIO
requests.

Change the single tracker (next_bypass_group) to an array of trackers based
on the number of data disks in a row of the RAID map.

Link: https://lore.kernel.org/r/164375212842.440833.6733971458765002128.stgit@brunhilda.pdev.netReviewed-by: Kevin Barnett <kevin.barnett@microchip.com>
Reviewed-by: Mike McGowen <mike.mcgowen@microchip.com>
Reviewed-by: Scott Benesh <scott.benesh@microchip.com>
Reviewed-by: Scott Teel <scott.teel@microchip.com>
Signed-off-by: Mike McGowen <Mike.McGowen@microchip.com>
Signed-off-by: Don Brace <don.brace@microchip.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>