CA-110805: Add a function to find the host's VGA device

Signed-off-by: John Else <john.else@citrix.com>
CA-110805: Blacklist the system display device rather than creating a PGPU for it

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1443 from johnelse/ca-110805

Don't create a PGPU or GPU_group for the system display device