block: cgroups, kconfig, build bits for BFQ-v7r5-3.1

From 41059122900f1deaa17d2572b0803c7b6b3f964e Mon Sep 17 00:00:00 2001
From: Paolo Valente <paolo.valente@unimore.it>
Date: Mon, 19 Dec 2011 16:34:01 +0100

Add a Kconfig option and do the related Makefile changes to compile
the BFQ I/O scheduler.  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>