Extra makefile for nil port

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7019 35acf78f-673a-0410-8e92-d51de3d6d3f4
Fixed setup_context and removed unused extctx

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7020 35acf78f-673a-0410-8e92-d51de3d6d3f4
Fixed indexing of context offset inside thread_t (was chibios's thread_t based...)

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7021 35acf78f-673a-0410-8e92-d51de3d6d3f4
Add initial nil-avr demo

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7022 35acf78f-673a-0410-8e92-d51de3d6d3f4