radeonsi/virtio: support vpipe

For now use an environment variable to test the virtio code
using vpipe.

Exposing DRM_PRIME_CAP_EXPORT manually is required, otherwise
gbm platform will fallback to dummy buffers which aren't
supported.

Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Acked-by: Rob Clark <robdclark@chromium.org>
Acked-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34470>

src/gallium/drivers/radeonsi/si_get.c

@@ -16,6 +16,7 @@
 #include "util/u_video.h"
 #include "vl/vl_video_buffer.h"
 #include <sys/utsname.h>
+#include "drm-uapi/drm.h"
 
 /* The capabilities reported by the kernel has priority
    over the existing logic in si_get_video_param */
@@ -1148,6 +1149,11 @@ void si_init_screen_caps(struct si_screen *sscreen)
    caps->cl_gl_sharing = true;
    caps->call_finalize_nir_in_linker = true;
 
+   /* Fixup dmabuf caps for the virtio + vpipe case (when fd=-1, u_init_pipe_screen_caps
+    * fails to set this capability). */
+   if (sscreen->info.is_virtio)
+         caps->dmabuf |= DRM_PRIME_CAP_EXPORT | DRM_PRIME_CAP_IMPORT;
+
    caps->fbfetch = 1;
 
    /* Tahiti and Verde only: reduction mode is unsupported due to a bug

src/gallium/drivers/radeonsi/si_pipe.c

@@ -1664,6 +1664,8 @@ struct pipe_screen *radeonsi_screen_create(int fd, const struct pipe_screen_conf
 #ifdef HAVE_AMDGPU_VIRTIO
    if (strcmp(version->name, "virtio_gpu") == 0) {
       rw = amdgpu_winsys_create(fd, config, radeonsi_screen_create_impl, true);
+   } else if (debug_get_bool_option("AMD_FORCE_VPIPE", false)) {
+      rw = amdgpu_winsys_create(-1, config, radeonsi_screen_create_impl, true);
    } else
 #endif
    {