libtasn dependencies are specific to the trust module, add a PACKAGECONFIG
for that and move the dependencies. This is currently enabled by default
to preserve behaviour.
p11-kit has optional systemd user units for the remote server, add a
PACKAGECONFIG for that that respects the systemd DISTRO_FEATURE.
Signed-off-by: Ross Burton <ross.burton@arm.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>