openglcontrol: added Red,Green,Blue bits for target gtk

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40229 4005530d-fff6-0310-9dd1-cebe43e6787f
openglcontrol: changed default DepthBits to 24

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@40230 4005530d-fff6-0310-9dd1-cebe43e6787f