Servo: V3: Allow for non-FTDI Interfaces

This is the initial work to begin implementing Servo V3 interfaces.

First INTERFACE_DEFAULTS and SERVO_ID_DEFAULTS was refactored out
of ftdi_common.

Modified existing interface init functions to be specifically for
ftdi and added new barebone init functions for beaglebone interfaces.

Created skeleton classes for beaglebone interfaces and filed bugs
to actually implement them.

BUG=chromium-os:39171
TEST=ensured servod and dut-control still work for servo-V2

Change-Id: I632e66f971c0b95253c24ba69427890220a3a4a6
Reviewed-on: https://gerrit.chromium.org/gerrit/45368
Reviewed-by: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Simran Basi <sbasi@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Tested-by: Simran Basi <sbasi@chromium.org>
7 files changed