Expand Refclk API's

[NateMeyer]

Different devices support a variety of configurations for refclk in and out. Survey available devices and add supporting API to configure them.

[azonenberg]

Frequencies:

• Some old HP gear: 5 MHz
• Old telco gear: 2.048 MHz
• High end: 100 MHz
• LeCroy labMaster is 10 GHz??
• Some R&S: 1 MHz to 20 MHz in 1 Hz steps

Connector schemes:

• None
• Unidirectional input
• Unidirectional output
• Bidirectional I/O with manual direction control
• Bidirectional I/O with auto sensing?? (misunderstood OP, have not seen an example of this in the wild yet)