drivers: bus: simple-pm-bus: Add support for probing simple bus only devices

fw_devlink could end up creating device links for bus only devices.
However, bus only devices don't get probed and can block probe() or
sync_state() [1] call backs of other devices. To avoid this, probe these
devices using the simple-pm-bus driver.

However, there are instances of devices that are not simple buses (they get
probed by their specific drivers) that also list the "simple-bus" (or other
bus only compatible strings) in their compatible property to automatically
populate their child devices. We still want these devices to get probed by
their specific drivers. So, we make sure this driver only probes devices
that are only buses.

[1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/

Fixes: c442a0d18744 ("driver core: Set fw_devlink to "permissive" behavior by default")
Cc: stable <stable@vger.kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Tested-by: Saravana Kannan <saravanak@google.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20210929000735.585237-2-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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