anv: Use DRM sync objects to back fences whenever possible

In order to implement VK_KHR_external_fence, we need to back our fences
with something that's shareable.  Since the kernel wait interface for
sync objects already supports waiting for multiple fences in one go, it
makes anv_WaitForFences much simpler if we only have one type of fence.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/intel/vulkan/anv_device.c

@@ -339,6 +339,8 @@ anv_physical_device_init(struct anv_physical_device *device,
    device->has_exec_async = anv_gem_get_param(fd, I915_PARAM_HAS_EXEC_ASYNC);
    device->has_exec_fence = anv_gem_get_param(fd, I915_PARAM_HAS_EXEC_FENCE);
    device->has_syncobj = anv_gem_get_param(fd, I915_PARAM_HAS_EXEC_FENCE_ARRAY);
+   device->has_syncobj_wait = device->has_syncobj &&
+                              anv_gem_supports_syncobj_wait(fd);
 
    bool swizzled = anv_gem_get_bit6_swizzle(fd, I915_TILING_X);