iwlwifi: dbg: move debug data to a struct

The debug variables are bloating the iwl_fw struct.  And the fields
are out of order, missing docs and some are redundant.

Clean this up.  This serves as preparation for unionizing it for the
new ini infra.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>