This sets the ARCH and PART_ID environment variables so that the
selected part family is used for simulations by default. This can be
overridden by changing them in the Makefile for the testbench if a
testbench requires a specific part family. Prior to this change, the
default was always ARCH=kintex7, PART_ID=xc7k410t/ffg900/-2, which
required support for that part to be installed.
Original-commit: c176046dff4941bcec27b0b72e5a68264c4808e5
Humberto Jimenez