This commit add helpers to create and to import a DmaBuf via the
external_dmabuf_info struct.
The import path is based on the image creation of wlroots and the create path is
inspired by the wlroots vulkan allocator MR.
vulkan_wait_idle waits until the device is idle and all referenced
objects can be destroyed.
vulkan_wait_fence waits until a fence is triggered by a finished
queueSubmit.
vulkan: wait on fence
This commit should just shuffle code around with no functional changes.
The goal is to ease development of simple vulkan nodes by providing
generic helpers.
