deskutils/griffith: Set LXML option by default

This port is unmaintained. The referenced PR indicates that LXML
dependency is not actually optional and run-time files if it's not
installed. If true, it should be installed unconditionally, but as
a half-measure, I'll just switch the option to fix it for standard
binary packages, and let the future maintainer look into this more.

PR: 194151
Submitted by: ktullavik (gmail)