isci: uplevel request infrastructure

* Consolidate tiny header files
* Move files out of core/ (drop core/scic_sds_ prefix)
* Merge core/scic_sds_request.[ch] into request.[ch]
* Cleanup request.c namespace (clean forward declarations and global
  namespace pollution)

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

drivers/scsi/isci/task.c

@@ -56,15 +56,12 @@
 #include <linux/completion.h>
 #include <linux/irqflags.h>
 #include "sas.h"
-#include "scic_task_request.h"
-#include "scic_io_request.h"
 #include "remote_device.h"
 #include "remote_node_context.h"
 #include "isci.h"
 #include "request.h"
 #include "sata.h"
 #include "task.h"
-#include "scic_sds_request.h"
 #include "timers.h"
 
 /**