Add high-speed device support in FT2232 driver:

- Initial support for FT2232H/FT4232H devices from FTDI.
- Add --enable-ftd2xx-highspeed option to configure script.
- Original patch submitted by Joern Kaipf <lists@joernline.de>.


git-svn-id: svn://svn.berlios.de/openocd/trunk@1998 b42882b7-edfa-0310-969c-e2dbd0fdcd60