[vioscsi] Programmatically determine max_segments

Refactors VioScsiFindAdapter() to:

1.  Use new mnemonic adaptExt->max_segments to replace adaptExt->max_physical_breaks
    (also used in the VioScsiBuildIo() and VioScsiReadExtendedData() functions)
2.  Enable Registry lookup for max_segments in neo value "MaxPhysicalSegments" or
    the legacy value "PhysicalBreaks". New value defined by REGISTRY_MAX_PH_SEGMENTS.
3.  Also derive max_segments from adaptExt->scsi_config.seg_max and also from
    the adaptExt->scsi_config.max_sectors value
4.  Choose from among best candidates and check within limits
5.  Enforce legacy StorPort NOPB off-by-one behaviour and provide explanation
6.  Improves relevant instrumentation
7.  Use new mnemonic PHYS_SEGMENTS_LIMIT to replace MAX_PHYS_SEGMENTS
8.  Update VIRTIO_MAX_SG to (PHYS_SEGMENTS_LIMIT + 1)
9.  Update VIRTIO_SCSI_QUEUE_LAST to (MAX_CPU - VIRTIO_SCSI_REQUEST_QUEUE_0)
10. Removed max_segments increment from calculation of sgMaxElements in VioScsiBuildIo()

Note: This commit enables the use of max_segments greater than
      adaptExt->scsi_config.seg_max (max = 254) up to
      PHYS_SEGMENTS_LIMIT (presently 512).

Signed-off-by: benyamin-codez <[email protected]>