Use descriptive constants, more

Marlin/Marlin_main.cpp

       }
       else
       {
-        bool all_axis = !((code_seen(axis_codes[0])) || (code_seen(axis_codes[1])) || (code_seen(axis_codes[2]))|| (code_seen(axis_codes[3])));
+        bool all_axis = !((code_seen(axis_codes[X_AXIS])) || (code_seen(axis_codes[Y_AXIS])) || (code_seen(axis_codes[Z_AXIS]))|| (code_seen(axis_codes[E_AXIS])));
         if(all_axis)
         {
           st_synchronize();