initial port
Multiple changes

- added GPIO driver to XMC4000
- new functions for the PIO module / updated docs
Identify not present GPIO ports

Ports with a number of pins equal to 0 are now considered as not
present on the host. This allows for a non-linear definition of
ports (for example: P0, P1, P3, P7, P8 ...)
xmc4000: fix number of ports/pins
merged github master
STM32F4 initial code import

Original authors:
* Zhanjun: http://dd.homeunix.com/home/space.php?uid=1&do=blog&id=90
* Ned Konz : https://github.com/bikeNomad
Various fixes in STM32F4 code
STM32F4 fixes

- added STM32-P407 board from Olimex (no ext SRAM yet)
- added documentation for the new configurator parameters

Signed-off-by: Bogdan Marinescu <bogdan.marinescu@gmail.com>
this should've been part of previous commit
Added support for STM32-E407 (Olimex)
fix for previous commit
Apply patch that was still only in jsnyder branch:
- Enable use of internal voltage reference and temperature sensor
stm32f4: added backend-specific UART pin configuration mechanism
Added support for STM32 PORT407z
http://www.wvshare.com/product/Port407Z.htm
Adding support for STM32F4 on master