BACKPORT: driver core: Add waiting_for_supplier sysfs file for devices

This would be useful to check if a device is not probing because it's
waiting for a supplier to be added and then linked to before it can
probe.

To reduce sysfs clutter, this file is added only if it can ever be 1.
So, if fw_devlink is disabled or set to permissive, this file is not
added. Also, this file is removed once the device probes as it's no
longer relevant.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20200521191800.136035-4-saravanak@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit da6d647598a6d182eb6a0344a7b14ae005244399)
[Conflicts due to missing fw_devlink_is_permissive() and fw_devlink_flags]
Signed-off-by: Saravana Kannan <saravanak@google.com>
Bug: 163090256
Change-Id: Ief4b9e35aff600f2eb88d15839e98a610f1c252f