Add a timeout parameter to blocking serial calls.

Add a timeout parameter to blocking serial calls.

Set this new parameter to 0 (no timeout) at every call site. This is
consistent with previous behaviour, so cannot cause any regressions.

Waiting forever for a serial operation is clearly always wrong. Without
specific knowledge of each device and driver however, I can't choose
appropriate timeouts for each call. The maintainers of these drivers
will need to do so, and also add appropriate handling of timeouts.

When this commit is merged, a bug should be entered for each driver
that is touched by it.