driver core: Add flag to autoremove device link on supplier unbind

Add a flag to autoremove the device links on supplier driver
unbind. This obviates the need to explicitly delete the link
in the remove path.
We remove these links only when the supplier's link to its
consumers has gone to DL_STATE_SUPPLIER_UNBIND state.

Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Suggested-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>