strongswan: split PKI tool into separate package

strongswan: split PKI tool into separate package

We currently include the PKI tool in strongswan-utils, which is a
dependency of the strongswan-default meta-package. As it's generally not
recommended to generate keys on embedded devices due to lack of entropy,
move the PKI tool to a separate package, and only depend on it in the
strongswan-full meta-package.

While at it, add pki.conf to the package.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>