e1000e: cosmetic move of #defines and prototypes to the new 82571.h

Move #defines and function prototypes specific to the 8257x family of
devices (82571, 82572, 82573, 82574, 82583) to the new 82571.h header file
(the convention for Intel wired ethernet drivers is to use the name of the
first device in the family for related file and function names).  These
defines and function prototypes can be used by other files in the driver
and moving them to the 8257x-family-specific file makes it clearer to which
devices 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>