UPSTREAM: driver core: Add state_synced sysfs file for devices that support it

This can be used to check if a device supports sync_state() callbacks
and therefore keeps resources left on by the bootloader enabled till all
its consumers have probed.

This can also be used to check if sync_state() has been called for a
device or whether it is still trying to keep resources enabled because
they were left enabled by the bootloader and all its consumers haven't
probed yet.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20200521191800.136035-3-saravanak@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 8fd456ec0cf03875908d6b67c1cd20cf0a7b4474)
Signed-off-by: Saravana Kannan <saravanak@google.com>
Bug: 163090256
Change-Id: I15b6db469e545eed9ecc97aca02ea90e7d318f2c