drm/i915/gvt: Save/restore HW status to support GVT suspend/resume

drm/i915/gvt: Save/restore HW status to support GVT suspend/resume

This patch save/restore necessary GVT info during i915 suspend/resume so
that GVT enabled QEMU VM can continue running.

Only GGTT and fence regs are saved/restored now. GVT will save GGTT
entries on each host_entry update, restore the saved dirty entries
and re-init fence regs in resume routine.

V2:
- Change kzalloc/kfree to vzalloc/vfree since the space allocated
from kmalloc may not enough for all saved GGTT entries.
- Keep gvt suspend/resume wrapper in intel_gvt.h/intel_gvt.c and
move the actual implementation to gvt.h/gvt.c. (zhenyu)
- Check gvt config on and active with intel_gvt_active(). (zhenyu)

V3: (zhenyu)
- Incorrect copy length. Should be num entries * entry size.
- Use memcpy_toio()/memcpy_fromio() instead of memcpy for iomem.
- Add F_PM_SAVE flags to indicate which MMIOs to save/restore for PM.

V4:
Rebase.

V5:
Fail intel_gvt_save_ggtt as -ENOMEM if fail to alloc memory to save
ggtt. Free allocated ggtt_entries on failure.

V6:
Save host entry to per-vGPU gtt.ggtt_mm on each host_entry update.

V7:
Restore GGTT entry based on present bit.
Split fence restore and mmio restore in different functions.

Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Hang Yuan <hang.yuan@linux.intel.com>
Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20201027045308.158955-1-colin.xu@intel.com