sfc_ef100: extend ef100_check_caps to cover datapath_caps3

MC_CMD_GET_CAPABILITIES now has a third word of flags; extend the
 efx_has_cap() machinery to cover it.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>