Since OpenImageDenoise requires a CPU with SSE 4.1 or newer,
let the node act as passthrough on unsupported CPUs and display
a message in the node itself.
Running multiple instances of OIDN simultaneously can use dozens
of GBs of memory. Since OIDN is multithreaded internally, we can run
only one instance at a time and should not lose much performance.
Fixing T69006