virtio: gpu: forward use_external_blob flag to renderer
virtio: gpu: forward use_external_blob flag to renderer

Fixes crosvm's failure to forward the "use_external_blob"
state flag to the host renderer (virglrenderer).

BUG=b:174794821
TEST=Start a crostini VM and run `DISPLAY=:0 glxgears`, verify graphical
output.

Change-Id: I1ef616079664224e7741cea00b9125c5061ea69d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2574669
Tested-by: Ryan Neph <7a140012b58874b966883fce003938f5de9942f2@google.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Gurchetan Singh <99434bba058e25b6203b8ae055a4f697dad0ef64@chromium.org>
Commit-Queue: Ryan Neph <7a140012b58874b966883fce003938f5de9942f2@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm