mpt3sas: Make use of additional HighPriority credit message frames for sending SCSI...

mpt3sas: Make use of additional HighPriority credit message frames for sending SCSI IO's

BugLink: http://bugs.launchpad.net/bugs/1512221
Driver assumes HighPriority credit as part of Global credit. But,
Firmware treats HighPriority credit value and global cedits as two
different values. Changed host queue algorithm to treat global credits
and highPriority credits as two different values.

Signed-off-by: Suganath prabu Subramani <suganath-prabu.subramani@avagotech.com>
Signed-off-by: Chaitra P B <chaitra.basappa@avagotech.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from commit 3ffa7c60b71fcd1070a68a74c380c05c4c161710)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>