radv/winsys: do not try to create a BO list with 0 buffers

radv/winsys: do not try to create a BO list with 0 buffers

This happens when all BOs have the RADEON_FLAG_NO_INTERPROCESS_SHARING
(DRM version >= 3.23) flag set. This flag is mainly used for reducing
overhead on the userspace side because we don't have to put those BOs
inside the list.

Though, if the driver tries to create a list with 0 buffers inside it,
libdrm returns -EINVAL and the app just crashes.

This fixes a bunch of CTS dEQP-VK.sparse_resources.* fails (~100).

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>