e1000e: cosmetic move of #defines and function prototypes to the new nvm.h

Move #defines and function prototypes which are applicable to all/most
devices supported by the driver and are specific to the NVM component of
each device to the new nvm.h header file.  These #defines and function
prototypes can be used by other files in the driver and moving them to the
NVM-specific file makes it clearer to which component they are applicable.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>