mfd: omap-usb-host: Fix dts probe of children

It currently only works if the parent bus uses "simple-bus". We
currently try to probe children with non-existing compatible values.
And we're missing .probe.

I noticed this while testing devices configured to probe using ti-sysc
interconnect target module driver. For that we also may want to rebind
the driver, so let's remove __init and __exit.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>