iwlwifi: clean up register names and defines

This patch cleans up and renames some of the SCD registers.
 It move SCD definitions into iwl-prhp.h file

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>