isci: remove base_request abstraction

Merge struct sci_base_request into scic_sds_request, and also factor the two
types of state machine handlers into one function.  While we're at it also
remove lots of duplicate incorrect kerneldoc comments for the state machine
handlers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>