rutabaga_gfx: virglrenderer: fix context_create_fence flag incompatibility
rutabaga_gfx: virglrenderer: fix context_create_fence flag incompatibility

Virglrenderer interprets flag fences differently from crosvm, but this
path hasn't been used until the upcoming support for multiple timelines
in Venus. Virglrenderer's render_server assumes that only
VIRGL_RENDERER_FENCE_FLAG_MERGEABLE is set, but before this CL, we
mistakenly pass (RUTABAGA_FLAG_FENCE | RUTABAGA_FLAG_INFO_RING_IDX),
which match the similarly named VIRTIO_GPU_* flags passed by the guest
virtio-gpu kernel driver. Then render_server blows up...

BUG=b:258854534
TEST=vkcube in VM after supporting Venus multiple timelines

Change-Id: I778d9767882aaf820fb7c8cdd9d37dab75fefcf0
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/4024080
Reviewed-by: Yiwei Zhang <8740d9f1664e48d07df551c300bbdb1ae03f6b48@chromium.org>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Commit-Queue: Ryan Neph <7a140012b58874b966883fce003938f5de9942f2@google.com>

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