net/sfc: move event support init to attach stage

Prepare to fix device reconfigure.
Device arguments should be parsed once on attach.
Management event queue should be initialized once on attach.

Fixes: 58294ee65afb ("net/sfc: support event queue")
Fixes: c22d3c508e0c ("net/sfc: support parameter to choose performance profile")
Cc: stable@dpdk.org
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@solarflare.com>