firewire-lib: move AV/C General command to

Some commands in AV/C Digital Interface Command Set General Specification
Version 4.2 are used by many devices. This commit move commands below from
bebob to firewire-lib:
 - avc_general_set_sig_fmt(): for setting sampling frequency
 - avc_general_get_sig_fmt(): for getting sampling frequency
 - avc_general_get_plug_info(): for get the number of plugs
bebob: add check byte flag for fcp_avc_transaction()
bebob: rename terratek to terratec
firewire-lib: add read in dualwire mode support

Dice chipset has a mode named as 'dualwire' for its streaming with high sampling
rate. In this mode, the rate of streaming is a half than setting and the size of
data block in a AMDTP packet is double than usual.

This commit add support for transmit stream (in stream) and fix some bugs...