driver-core: add driver module asynchronous probe support

Some init systems may wish to express the desire to have device
drivers run their probe() code asynchronously.
This implements support for this and allows userspace to request
async probe as a preference through a generic shared device driver
module parameter, async_probe.

Implementation for async probe is supported through a module
parameter given that since synchronous probe has been prevalent
for years some userspace might exist which relies on the fact that
the device driver will probe synchronously and the assumption that
devices it provides will be immediately available after this.

Change-Id: Ic20ee2354b2efdcf3c0d02c407863af559ff86fa
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: f2411da746985e60d4d087f3a43e271c61785927
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>