intel_de3815: initial support for Baytrail NUC

* I2C only currently supported, Both bus 0 and 1

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>
de3815: added PWM support

There are two PWM pins on the custom solutions header.
10-PWM[0] and 11-PWM[1] in mraa.

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>
de3815: add initial doc

Also removed printf used during inital implementation.

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>