iwlwifi: move all NVM parsing code to the common files

Move all the NVM file handling code to iwl-nvm-parse.c where all this
stuff belongs.  This cleans up the MVM specific code and allows easier
reuse by other opmodes if needed.

Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>