ext: dsent: adds a Python interface, drops C++ one
This patch extensively modifies DSENT so that it can be accessed using Python.
To access the Python interface, DSENT needs to compiled as a shared library.
For this purpose a CMakeLists.txt file has been added. Some of the code that
is not required is being removed.

ext: add the source code for DSENT
This patch adds a tool called DSENT to the ext/ directory. DSENT
is a tool that models power and area for on-chip networks. The next
patch adds a script for using the tool.