pf_key/xfrm_algo: prepare pf_key and xfrm_algo for new algorithms without pfkey support

Mark existing algorithms as pfkey supported and make pfkey only use algorithms
that have pfkey_supported set.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>