There was a recent change in Intel's driver that triggered a driver-internal
error if the semaphore given to the command buffer wasn't initialized.
Given that the specifications require the semaphore to be initialized,
this is within spec. Unlike what's causing it in the first place, which is
that there are no ways to extract/import dma sync objects from DMABUFs,
so we must leave our semaphores bare.
This commit adds the necessary code to initialize and use a Vulkan device
within the hwcontext libavutil framework.
Currently direct mapping to VAAPI and DRM frames is functional, and
transfers to CUDA and native frames are supported.
Lets hope the future Vulkan video decode extension fits well within this
framework.
