iwlwifi: HW dependent run time calibration

This patch does several things:

1) rename CONFIG_IWL4965_SENSITIVITY to IWL4965_RUN_TIME_CALIB which is
   better semantic
2) move all the run time calibration to a new file: iwl-calib.c
3) simplify the sensitivity calibration flow and make it HW dependent
4) make the chain noise calibration flow HW dependent

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>