wl1271: moved scan operations to a separate file

The scanning code is going to get a bit more complex, with proper support for
active/passive scans together with 2.4GHz and 5GHz.  In the future, also a
new type of scan (periodic scan) will be added.  When all this is
implemented, the code is going to be much more complex, so we'd better
separate it into a separate file.

This patch doesn't have any impact on functionality.

Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Reviewed-by: Saravanan Dhanabal <ext-saravanan.dhanabal@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>