iwlwifi: split out firmware store

Through the driver, struct iwl_fw will
store the firmware. Split this out into
a separate file, iwl-fw.h, and make all
other code use it. To do this, also move
the log pointers into it, and remove the
knowledge of "nic" from everything.

Now the op_mode has a fw pointer, and
(unfortunately) for now the shared data
also needs to keep one for the transport
to access dump the error log -- I think
that will move later.

Since I wanted to constify the firmware
pointers, some more changes were needed.

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