main/p11-kit: Ensure trust_paths is set

During the upgrade from `0.23.18.1-r0` to `0.23.20-r0` in commit
7aef1583, the build system was changed
from autotools to meson, but the `--with-trust-paths` option didn't get
ported over to the meson equivalent.

This caused commands, like `trust list`, to return no results, which
causes Java issues due to `/etc/ssl/certs/java/cacerts` not being
updated properly (#11185).

This commit adds the meson `trust_paths` build variable so that p11-kit
can find the proper CA certs file.

Signed-off-by: Andrew Gunnerson <andrew.gunnerson@us.ibm.com>