crosvm: clearer naming about GPU features

It's possible to compile the gpu device without virgl_renderer.
In fact, in many instances, this may be required.

This builds the gpu device default, but only with --gpu do I see
/dev/dri/renderN128, so this should be safe.

BUG=b:173630595
TEST=compile and run

Cq-Depend: chromium:2592111
Change-Id: I5fbf2de8a2f818a9ca2e5ac4a1a02c7797cff927
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2592089
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Daniel Verkamp <dverkamp@chromium.org>
Auto-Submit: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Commit-Queue: Gurchetan Singh <gurchetansingh@chromium.org>
diff --git a/Cargo.toml b/Cargo.toml
index 4a2eccd..be8e5e4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -31,7 +31,7 @@
 ]
 
 [features]
-default = ["audio"]
+default = ["audio", "gpu"]
 chromeos = ["base/chromeos"]
 default-no-sandbox = []
 audio = ["devices/audio"]
@@ -43,8 +43,9 @@
 video-encoder = ["devices/video-encoder"]
 wl-dmabuf = ["devices/wl-dmabuf", "gpu_buffer", "resources/wl-dmabuf"]
 x = ["devices/x"]
-virtio-gpu-next = ["rutabaga_gfx/virtio-gpu-next"]
+virgl_renderer_next = ["rutabaga_gfx/virgl_renderer_next"]
 composite-disk = ["protos/composite-disk", "protobuf", "disk/composite-disk"]
+virgl_renderer = ["devices/virgl_renderer"]
 gfxstream = ["devices/gfxstream"]
 gdb = ["gdbstub", "thiserror",  "arch/gdb", "vm_control/gdb", "x86_64/gdb"]