added a header file that maps from MCU pins to Arduino
pin numbers

* also added a trailing underscore to header guards for consistency

Commit for PR 2623, repairing header file include guards.
This PR is intended to fix the include guards in files under RIOT/boards

SQUASH ME: fix underscore removal overdos

SQUASH ME: consistent macro naming

SQUASH ME: missed that one

SQUASH ME: fixed overdo

SQUASH ME: consistency

- changed naming of cortexm_common in makefiles
- included some minor cleanups

fix functions arguments

extended sam3x GPIO from 16 to 31

fix GPIO_NUMOF to 32

add GPIOs

extend GPIO 16-31  for ArduinoDue/UDOO

fix white space at the end  gpio_clear

The file was accidentally changed in 23626234

Cortex-M processors only support Thumb instructions (no ARM mode code).

Signed-off-by: Joakim Gebart <joakim.gebart@eistec.se>

- added port defines to periph_conf.h
- added feature to Makefile.features

This change allows drivers (or any module for that matter) to provide
features. This is e.g. useful if a board does not have a transceiver,
but your application uses `USEMODULE += some_driver`, which implements
the transceiver interface.

The line `FEATURES_PROVIDED += some_feature` should go to the guarded
block in `{sys,drivers}/Makefile.include`.

doxygen does a good job itself, identifying the unique part of the path
to identify a file.