[AVR] Fixed checking for tickless mode

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7518 35acf78f-673a-0410-8e92-d51de3d6d3f4
[AVR] Updated PWM driver for 3.0 compatibility

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7519 35acf78f-673a-0410-8e92-d51de3d6d3f4