Setting up default iosched in 5.0+

[Alexey Dobriyan]

5.0 deleted three io schedulers and more importantly CONFIG_DEFAULT_IOSCHED
option:

	commit f382fb0bcef4c37dc049e9f6963e3baf204d815c
	block: remove legacy IO schedulers

After figuring out that I silently became "noop" customer enabling just
BFQ didn't work: "noop" is still being selected by default.

There is an "elevator=" command line option but it does nothing.

Are users supposed to add stuff to init scripts now?