drm/xe: Store xe_hw_engine in xe_hw_engine_snapshot

A future patch will require gt and xe device structs, so here
replacing class by hwe.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Zhanjun Dong <zhanjun.dong@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240424140319.61651-1-jose.souza@intel.com