drm/virtio: New fence for every plane update

Having a fence linked to a virtio_gpu_framebuffer in the plane update
sequence would cause conflict when several planes referencing the same
framebuffer (e.g. Xorg screen covering multi-displays configured for an
extended mode) and those planes are updated concurrently. So it is needed
to allocate a fence for every plane state instead of the framebuffer.

Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
[dmitry.osipenko@collabora.com: rebase, fix up, edit commit message]
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241020230803.247419-2-dmitry.osipenko@collabora.com