block: Update BFQ from v7r4 to v7r5

v7r5:
. IMPROVEMENT: Improve throughput boosting by idling the device
  only for processes that, in addition to perform sequential I/O,
  are I/O-bound (apart from weight-raised queues, for which idling
  is always performed to guarantee them a low latency).
. IMPROVEMENT: Improve throughput boosting by depriving processes
  that cooperate often of weight-raising.
. CODE IMPROVEMENT: Pass of improvement of the readability of both
  comments and actual code.

Signed-off-by: Chet Kener <Cl3Kener@gmail.com>