e1000e: cosmetic move of function prototypes to the new mac.h

Move prototypes for functions which are applicable to all/most devices
supported by the driver and are specific to the MAC component of each
device to the new mac.h header file.  These function prototypes can be used
by other files in the driver and moving them to the MAC-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>