Add PNP info to PCI attachment of gem driver

Move device table earlier in the file so we can reference it in the
PNP_INFO macro.

Reviewed by: imp, chuck
Submitted by: Lakhan Shiva Kamireddy <lakhanshiva@gmail.com>
Sponsored by: Google, Inc. (GSoC 2018)
Pull Request: https://github.com/bsdimp/freebsd/pull/5