drm/xe/pf: Add minimal support for VF_STATE_NOTIFY events

GuC will use VF_STATE_NOTIFY events to notify the PF about changes
of the VF state, in particular when a VF FLR was requested. Add
very minimal support for such events to avoid reporting errors due
to unexpected G2H. We will improve handling of these messages later.

While around also add few basic functions to control the VF state
(pause, resume, stop) as we will also exercise them soon.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240326191518.363-3-michal.wajdeczko@intel.com