[KINETIS] Fix K20 serial driver

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7149 35acf78f-673a-0410-8e92-d51de3d6d3f4
[KINETIS] Add serial support to K20D50M demo + TestThread

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7150 35acf78f-673a-0410-8e92-d51de3d6d3f4