Add OPTIONS to some kde@ ports.

For best runtime performance (e.g. a fully functional desktop), users will
need a pinentry application -- pinentry-qt fits best into the KDE desktop,
but it could be a different one -- and sound output. Pick a default backend
and some OSS plugins to make that happen.

These are OPTIONS so the users interested in a minimal desktop or one with
different audio needs can build suitable packages themselves.

Reviewed by: tcberner
Differential Revision: https://reviews.freebsd.org/D18680