scsi: docs: convert arcmsr_spec.txt to ReST

scsi: docs: convert arcmsr_spec.txt to ReST

This file had its own peculiar style, not following any other
files inside the Kernel (as far as I saw).

Had to do a number of changes here, starting by removing the two
leading asterisks from each line, adding table and literal
block markups and changing whitespace and blank lines.

The end result is that (IMHO), it is now a lot easier to read
it as a text file, while producing a good html output.

Link: https://lore.kernel.org/r/6f8e4da4ea643adbe048f55504a59427c5e50c97.1583136624.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>