drm/i915: Enable guest i915 full ppgtt functionality

drm/i915: Enable guest i915 full ppgtt functionality

Enable the guest i915 full ppgtt functionality when host can provide this
capability. vgt_caps is introduced to guest i915 driver to get the vgpu
capabilities from the device model. VGT_CPAS_FULL_PPGTT is one of the
capabilities type to let guest i915 dirver know that the guest i915 full
ppgtt is supported by device model.

Notice that the minor version of pvinfo isn't bumped because of this
vgt_caps introduction, due to older guest would be broken by simply
increasing the pvinfo version. Although the pvinfo minor version doesn't
increase, the compatibility won't be blocked. The compatibility is ensured
by checking the value of caps field in pvinfo. Zero means no full ppgtt
support and BIT(2) means this feature is provided.

Changes since v1:
- Use u32 instead of uint32_t (Joonas)
- Move VGT_CAPS_FULL_PPGTT introduction to this patch and use #define
  instead of enum (Joonas)
- Rewrite the vgpu full ppgtt capability checking logic. (Joonas)
- Some coding style refine. (Joonas)

Changes since v2:
- Divide the whole patch set into two separate patch series, with one
  patch in i915 side to check guest i915 full ppgtt capability and enable
  it when this capability is supported by the device model, and the other
  one in gvt side which fixs the blocking issue and enables the device
  model to provide the capability to guest. And this patch focuses on guest
  i915 side. (Joonas)
- Change the title from "introduce vgt_caps to pvinfo" to
  "Enable guest i915 full ppgtt functionality". (Tina)

Change since v3:
- Add some comments about pvinfo caps and version. (Joonas)

Change since v4:
- Tested by Tina Zhang.

Change since v5:
- Add limitation about supporting 32bit full ppgtt.

Change since v6:
- Change the fallback to 48bit full ppgtt if i915.ppgtt_enable=2. (Zhenyu)

Change in v9:
- Remove the fixme comment due to no plan for 32bit full ppgtt
  support. (Zhenyu)
- Reorder the patch-set to fix compiling issue with git-bisect. (Zhenyu)
- Add print log when forcing guest 48bit full ppgtt. (Zhenyu)

v10:
- Update against Joonas's has_full_ppgtt and has_full_48bit_ppgtt disconnect
  change. (Zhenyu)

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> # in v2
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>