Add scheduled scan driver operations

Add scheduled scan driver operations

In new Linux kernel versions (>=3.0), nl80211 adds scheduled scan
capability. In order to use this feature to its full extent, we need
to support it in the wpa_supplicant core, so that it can also be used
by other drivers.

This commit adds initial scheduled scan support operations and events.

Signed-off-by: Luciano Coelho <coelho@ti.com>