drm/i915/gvt: Fix dma-buf display blur issue on CFL

drm/i915/gvt: Fix dma-buf display blur issue on CFL

Commit 7c81bc51596cc ("drm/i915/gvt: Enable gfx virtualiztion for CFL")
added the support on CFL. The vgpu emulation hotplug support on CFL was
supposed to be included in that patch. Without the vgpu emulation
hotplug support, the dma-buf based display gives us a blur face.

So fix this issue by adding the vgpu emulation hotplug support on CFL.

Fixes: 7c81bc51596cc ("drm/i915/gvt: Enable gfx virtualiztion for CFL")
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200227010041.32248-1-tina.zhang@intel.com
(cherry picked from commit 135dde8853c7e00f6002e710f7e4787ed8585c0e)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>