Add SIO I/O scheduler

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

Conflicts:
	block/Kconfig.iosched
	block/Makefile

Change-Id: I1b5b72757e9ddd535a74e65ddc38dfe815e7491d
Defconfig: enable SIO schedulers

Change-Id: Ie59bc67bbc322950f4f2c778fec88585ed59fad5