sfxge: add Medford firmware subtypes definitions

Pulled firmware_ids.h from firmwaresrc and applied genfwdef script.

Submitted by: Richard Houldsworth <rhouldsworth at solarflare.com>
Reviewed by: gnn
Sponsored by: Solarflare Communications, Inc.
MFC after: 2 days
Differential Revision: https://reviews.freebsd.org/D4897