[hdctools] servod: add miniservo functionality.

Miniservo is a smaller debug / control board that connects to the
Google debug header.  It provides uart access + 4 gpios via the FT232R
chip from FTDI.  This CL enables servod to recognize and instantiate
necessary interfaces to a connected miniservo.  This CL obsoletes the
previous prototype c-based server src/miniservod.c by providing a
nicer interface via dut-control and/or the servo autotest classes

Depends on:
CL: http://gerrit.chromium.org/gerrit/#change,1675

BUG=chrome-os-partner:2784
TEST=manual,
- Launch server
  sudo servod -c miniservo.xml -v 0x18d1 -p 0x5000
- investigate gpios
  dut-control
- connect to uart
  cu -l /dev/pts/XX

Similarily make sure servod still works by repeating client steps
above but by launching server with
  sudo servod -c servo.xml -v 0x18d1 -p 0x5001

Change-Id: I16921d89ea847397843c497a66c93672569219d8
Reviewed-on: http://gerrit.chromium.org/gerrit/8866
Tested-by: Todd Broch <tbroch@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
4 files changed