drm/xe/pf: Switch VF migration GuC save/restore to struct migration data

drm/xe/pf: Switch VF migration GuC save/restore to struct migration data

In upcoming changes, the GuC VF migration data will be handled as part
of separate SAVE/RESTORE states in VF control state machine.
Now that the data is decoupled from both guc_state debugfs and PAUSE
state, we can safely remove the struct xe_gt_sriov_state_snapshot and
modify the GuC save/restore functions to operate on struct
xe_sriov_migration_data.

Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patch.msgid.link/20251112132220.516975-16-michal.winiarski@intel.com
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>