MFC uftdi(4) driver changes...
  r264010: Support speeds up to 12mbaud on newer chips.
  r264031: Use 2K IO buffers for improved throughput.
  r264149: Add ioctl(2) calls to access bitbang, MPSSE, CPU_FIFO,
           and other modes.
MFC r264800: fixes for problems found by Coverity scan...
  - Get transmit loop more in line with the other serial drivers.
  - Add a comment about FTDI and ZLPs.
  - Correctly check odditiy of baud rate divisor.
  - Correct IOCTL handling for "error" and "event" char.
MFC r264018: update list of supported FTDI chips.