sfxge: add accessors for license-related MCDI calls to common code

Add support for Huntington MCDI licensing interface to common code.
Ported from Linux net driver IOCTL functions with restructuring for
initial support for V3 licensing API.

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/D4918