scpi-dmm: alpha-sort the list of supported devices (vendor/model list)

scpi-dmm: alpha-sort the list of supported devices (vendor/model list)

Any order is as arbitrary as any other. The alphabetical order of vendor
and model names might be the most robust during maintenance: easiest to
remember, easiest to use when checking for presence, and easiest to add
to or resolve conflicts during merges. Vendor renames (HP to Agilent to
Keysight, et al) are ugly but can't be helped easily.