drm/xe: Check pat.ops before dumping PAT settings

In the Linux kernel, the following vulnerability has been resolved:

drm/xe: Check pat.ops before dumping PAT settings

We may leave pat.ops unset when running on brand new platform or

when running as a VF. While the former is unlikely, the latter

is valid (future) use case and will cause NPD when someone will

try to dump PAT settings by debugfs.

It's better to check pointer to pat.ops instead of specific .dump

hook, as we have this hook always defined for every .ops variant.