Added AVR PWM test demo

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7023 35acf78f-673a-0410-8e92-d51de3d6d3f4
Fixed a warning

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7024 35acf78f-673a-0410-8e92-d51de3d6d3f4
Fixed warning

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7025 35acf78f-673a-0410-8e92-d51de3d6d3f4