[KINETIS] Initial K20 series header

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7131 35acf78f-673a-0410-8e92-d51de3d6d3f4
[KINETIS] Linker script and cmparams for K20

git-svn-id: svn://svn.code.sf.net/p/chibios/svn/trunk@7132 35acf78f-673a-0410-8e92-d51de3d6d3f4