We will need the full ra_ctx to be able to look up all the state
required to initialise an ffmpeg vulkan hwcontext, so pass let's
pass the ra_ctx instead of just the ra.
A longstanding pain point of the drm VOs is the relative lack of state
sharing. While drm_common does provide some sharing, it's far less than
other platforms like x11 or wayland. What we do here is essentially copy
them by creating a new vo_drm_state struct and using it in vo_drm and
context_drm_egl. Much of the functionality that was essentially
duplicated in both VOs/contexts is now reduced simple functions in
drm_common. The usage of the term 'kms' was also mostly eliminated since
this is libdrm nowadays from a userspace perspective.
We've had some annoying names for interops, which we can't simply
rename because that would break config files and command lines. So we
need to put a little more effort in and add a concept of legacy names
that allow us to continue loading them, but with a warning.
The two I'm renaming here are:
* vaapi-egl -> vaapi (vaapi works with Vulkan too)
* drmprime-drm -> drmprime-overlay (actually describes what it does)
* cuda-nvdec -> cuda (cuda interop is not nvdec specific)
