block: cgroups, kconfig, build bits for BFQ-v7r6-3.10.8+

Update Kconfig.iosched and do the related Makefile changes to include
kernel configuration options for BFQ. Also add the bfqio controller
to the cgroups subsystem.

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

Signed-off-by: Paul Reioux <reioux@gmail.com>

Change-Id: Ieae0bfda9ff88fd42dbeaa275b4182517342e2f9