block: prepare I/O context code for BFQ-v5r1 for 3.0

BFQ uses struct cfq_io_context to store its per-process per-device data,
reusing the same code for cic handling of CFQ.  The code is not shared
ATM to minimize the impact of these patches.

This patch introduces a new hlist to each io_context to store all the
cic's allocated by BFQ to allow calling the right destructor on module
unload; the radix tree used for cic lookup needs to be duplicated
because it can contain dead keys inserted by a scheduler and later
retrieved by the other one.

Update the io_context exit and free paths to take care also of
the BFQ cic's.

Change the type of cfqq inside struct cfq_io_context to void *
to use it also for BFQ per-queue data.

A new bfq-specific ioprio_changed field is necessary, too, to avoid
clobbering cfq's one, so switch ioprio_changed to a bitmap, with one
element per scheduler.

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

Conflicts:
	block/Kconfig.iosched
	block/Makefile
	block/blk-ioc.c
	block/cfq-iosched.c
	fs/ioprio.c
	include/linux/iocontext.h
block: Squashed update of BFQ-v5r1 to BFQ-v6

Conflicts:
	include/linux/iocontext.h
block: Squashed update of BFQ-v6 to BFQ-v6r1

- Introduce an eqm_lock to protect EQM-related data.
- Fix use-after-free of queues in __bfq_bfqq_expire(). It may happen that
  a call to bfq_del_bfqq_busy() puts the last reference taken on a queue
  and frees it. Subsequent accesses to that same queue would result in a
  use-after-free. Make sure that a queue that has just been deleted from
  busy is no more touched.
- Use the uninitialized_var() macro when needed. It may happen that a
  variable is initialized in a function that is called by the function
  that defined it. Use the uninitialized_var() macro in these cases.
Squashed update of BFQ-v6r1 to BFQ-v6r2
Enable BFQ

Signed-off-by: Nick0703 <lokesh.c703@gmail.com>