block: cgroups, kconfig, build bits for BFQ-v6r2 for 3.4

Update Kconfig.iosched to include kernel configuration options
for BFQ. Add a Kconfig option and do the related Makefile changes
to compile the scheduler. Also let the cgroups subsystem know about
the BFQ I/O controller.

Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>

Conflicts:
	block/Kconfig.iosched
	block/Makefile

Conflicts:
	block/Kconfig.iosched
	block/Makefile

Conflicts:
	block/Makefile

block: introduce the BFQ-v7r4 I/O sched for 3.4

block, bfq: add Early Queue Merge (EQM) to BFQ-v7r4 for 3.4.0"

block: bfq: Squashed update from BFQ-v7r4 to BFQ-v7r5

Change-Id: I749ef141246db7020cec0b10d980ec854a572603

bfq-iosched: Tuning for SSD

bfq-iosched: Set bfq_back_penalty = 1
block: Switch from BFQ-v7r5 for 3.4.0 to BFQ-v7r6 for 3.4.0

. IMPROVEMENT: Introduced a new mechanism that helps get the job done
  more quickly for services and applications that create or reactivate
  many parallel I/O-bound processes. Examples are systemd at boot, or
  commands such as git grep.
. CODE IMPROVEMENTS: Small code cleanups and improvements.

Change-Id: I69d00ba360f3b93b25c9f5a722cfe6d8a0df943b
Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
defconfig: enable bfq