iwlwifi: move scan to iwl-scan.c iwlcore

This patch moves scan code to iwl-scan.c file in iwlcore module.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>