drm/xe/vf: Document SRIOV VF restore flow

drm/xe/vf: Document SRIOV VF restore flow

This adds a documentation chapter, containing high level flow
of VF restore procedure.

v2: Better describe initial conditions, include GuC states on
  sequence diagram (Michal)
v3: moved DOC to .c (Michal)

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241104213449.1455694-3-tomasz.lis@intel.com
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>