scsi: docs: convert sym53c500_cs.txt to ReST

Link: https://lore.kernel.org/r/eff6166b3442ddb37b934bca46e7f9ef25ebc2a4.1583136624.git.mchehab+huawei@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>