block: add BFQv6 again
block/bfq-iosched.c: BFQ scheduler tweaks (thanks pkgnex from Franco's Dev Team)

Also fixed slice_idle limitation (credits to me)

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
block: cfq: definitely finally nail the CFQ tunables.
One final tweak to give us the desired 335, 85 on tuna, according to pkgnex's Excel GN equation which accomodates for the weird HZ: y=TRUNC(x*7.8125,0)