gamecontroller: Do less SDL polling when there aren't devices yet.

Until we have a device we shouldn't poll SDL as often to run up the
cpu. So until we get a device event only poll every 2 seconds.
After we get a device to watch start polling every 100ms.

This still significantly reduces how much we poll since before this we
were polling every 1 ms.

Signed-off-by: Jeremy Whiting <jpwhiting@kde.org>
(cherry picked from commit 6f956e62)