Minor issues with SG584 driver

The driver does not check if the HF option is avialable before adding parameters related to that

See https://www.thinksrs.com/downloads/pdfs/manuals/SG380m.pdf page 64. The rf doubler is needed for this to work correctly.

The lower frequency limit does not take the LF module into account

Start by locating the SG584 driver and reviewing how it adds HF-related parameters and calculates the lower frequency limit. Use the SG380m manual, page 64, to confirm the RF doubler and HF/LF module requirements; done means HF parameters are guarded by availability and the lower limit accounts for the LF module.

Written by the indexing model from the issue text.