artix7/make/project_xray.cmake: Allow prjxray path to be specified
artix7/make/project_xray.cmake: Allow prjxray path to be specified

Allow the path for prjxray-db to be specified as a source not within the
project or its submodules.

Signed-off-by: Nathan Rossi <2e8aa918660411855c6d44d5bb2da677aa033255@nathanrossi.com>

SymbiFlow/symbiflow-arch-defs,SymbiFlow/symbiflow-arch-defs