sfxge: change hunt specific fields of efx_nic_t to ef10

All these fields will be used in shared ef10 code, so put them in an
ef10 member of a per-architecture union, rather that in the per-chip
union.

Submitted by: Mark Spender <mspender at solarflare.com>
Reviewed by: gnn
Sponsored by: Solarflare Communications, Inc.
MFC after: 2 days
Differential Revision: https://reviews.freebsd.org/D4865