add smart-peripheral if, im2col acc, and Verifheep flow

[TommiTerza]

• Added a direct interface from external accelerators and the Always-On subsystem through a configurable reginterface bus (AOPB)
• Reworked the DMA channel structure
• Reworked the DMA HAL, increments are now in elements and not bytes
• Added configurable multi-master DMA-to-sysbus connection
• Added im2col Smart Peripheral Controller (SPC) and its application
• Added Verifheep, a python library for verification and testing of X-Heep on a variety of targets, FPGA included
• Added im2col SPC verification script based on Verifheep
• Updated the DMA documentation
• Added Verifheep documentation