egl: Allow software rendering for vgem/virtio_gpu in platform_device

Then user could explicitly choose the underlying device for software
rendering when both vgem/virtio_vga are there.

Signed-off-by: Lepton Wu <lepton@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5830>
1 file changed