reduce #ifdefs in Boards.h

[soundanalogous]

The arduino team is interested in reducing the number of microcontroller-specific #ifdef statements in core library files.

A number of the #ifdef statements in Boards.h can probably be removed for boards that have variant files in the Arduino IDE. What needs to be done here is a comprehensive audit of the variant files in Arduino as they related to the features requiring #ifdef statements in boards.h. The findings should be reported back to the Arduino team.

[soundanalogous]

see https://github.com/arduino/Arduino/issues/1621

[soundanalogous]

I should be able to switch to a few of the Frmata defined macros (in Boards.h) to Arduino defined macros.