databases/pgpool-II-40: Unbreak PAM option

The PAM option is tangled up with the SSL option in a weird way.
SSL_CONFIGURE_WITH is set once before bsd.port.options.mk for
enabling SSL support and overwritten again after including
bsd.port.options.mk but only when PAM=on.

Setting options helper after this point is not really supported,
but --with-pam actually makes it to CONFIGURE_ARGS. When options
helpers are processed the results are only realized later by make(1).
SSL_CONFIGURE_WITH has been defined before including bsd.port.options.mk,
so this sort of "works".

This, however, is presumably an implementation detail and enabling
the PAM option breaks SSL support since SSL_CONFIGURE_WITH is
overwritten with a new value: CONFIGURE_ARGS only has --with-pam
left and is missing --with-openssl.

PAM support does not depend on SSL support. Just switch everything
to options helpers to fix this.

PR: 234817
Submitted by: tobik
Approved by: tz (maintainer)