BugLink: http://bugs.launchpad.net/bugs/1544679

1. For iMR controllers, firmware will report two queue depths:

   - Controller-wide queue depth
   - LDIO queue depth (240)

Controller-wide queue depth will be greater among the two. Using this
new feature, iMR can provide larger Queue depth(QD) for JBOD and limited
QD for Virtual Disk(VD).

2. megaraid_sas driver will throttle read/write LDIOs based on "LDIO
Queue Depth".

3. Dual queue depth can be enabled/disabled via module parameter. It is
enabled by default if the firmware supports it. Only specific firmware
builds will enable the feature.

4. Added sysfs parameter "ldio_outstanding" which permits querying the
number of outstanding LDIO requests at runtime.
Signed-off-by: Sumit Saxena <sumit.saxena@avagotech.com>
Signed-off-by: Kashyap Desai <kashyap.desai@avagotech.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from linux-next commit 6516e25f7dc9f19d3a1138a1a9c19840f5962a48)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>