iwlwifi: clean up module parameters

For now at least, all module parameters should be
with the core functionality, so move them there,
while at it rename to iwlwifi_mod_params. Also
rename iwl-shared.h to iwl-modparams.h to reflect
the real contents.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>