Convert the btbridge to use the new IPMI D-Bus API

[tomjoseph83]

openbmc/kcsbridge@9ce5a9a

Along the lines of the above patch, the btbridge has to use the new IPMI D-Bus API which is method based instead of signal/method based.

[chrischen3-flex]

Hi @tomjoseph83,
Could you share how you know the "Channel number 0 is assigned to btbridge IPMI commands" in the source code? I have been stuck here for a long time. Thanks.