serial: Add function to extract serial options.

This patch adds a function for a common operation of all serial based drivers.
It extracts the serial options from the options linked list that is passed down
to every hardware driver.
hameg-hmo: Initial driver skeleton.
hameg-hmo: Add initial working driver version.

This patch adds initial support for Hameg's HMO oscilloscopes. It currently
supports only the HMO compact series (70MHz-200MHz).