[SCSI] mpt2sas: Basic Code Cleanup in mpt2sas_base

Basic Code Cleanup:
(1) _base_get_cb_idx and mpt2sas_base_free_smid were reorganized in
similar fashion so the order of obtaining the cbx and smid are
scsiio,
hi_priority, and internal.
(2) The hi_priority and internal request queue struct was made
smaller
by removing the scmd and chain_tracker, thus saving memory
allocation.
(3) For scsiio request, a new structure was created having the same
elements from the former request tracker struct.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>