bebob: add read-only "Clock Sync Status" control

Before changing clock source, some devices can tell whether detecting digital
input but the other devices can't tell it. After changing clock source, some
devices can tell its synchronization but the other can't.

This commit is for the latter devices. The users can check the status to
confirm synchronization.
bebob: add device specific operation for Focusrite Saffire series

I note that I have no devices in this series so need testers.

This commit add Switching clock source and hardware metering for this series of
device. The rest is changing sampling rate.