scsi: ufs: ufs device queue depth test

This test is trying to stress the edge cases of the UFS device queue.
This queue has two such edges, the total queue depth and the command per
LU. To test those edges properly, two deviations from the edge in addition
to the edge are tested as well. One deviation will be fixed (1), and the
second will be picked randomly.
The test will fill a request queue with random read requests. The amount
of request will vary each iteration and will be either the one of the
edges or the sum of this edge with one deviations.
Only reads or only writes will be tested within each iteration.

Change-Id: Ib02a63b2c8d6898f01e418a617ccc79eba67dab5
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>