scripts: check_init_priorities: ignore zephyr,cdc-acm-uart

The new stack zephyr,cdc-acm-uart driver has two separate init path, one
of which kicks in before the USB stack to start buffering log messages.

This generates a false positive in the build time priority checking,
adding a check to ignore that compatible entirely.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>