scsi: docs: convert libsas.txt to ReST

Link: https://lore.kernel.org/r/9022cb5551487f774cab16a828fe06b0b6b3add3.1583136624.git.mchehab+huawei@kernel.orgSigned-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Documentation/scsi/index.rst

@@ -23,5 +23,6 @@ Linux SCSI Subsystem
    g_NCR5380
    hpsa
    hptiop
+   libsas
 
    scsi_transport_srp/figures