This is the initial implementation based on DRM dumb buffers,
which cleans up various things at the same time:
- DRM output is separate from GBM and DRM dumb buffer displays.
The latter two re-use the former.
- The timer refresh for the Vulkan KHR Display rendering lives
now with the KHR display code, in hope to be replaced with a
better mechanism in the future.
What's missing still is support for partial updates as well as
rendering with our own software renderer.
This patch adds support for the `SLINT_KMS_ROTATION` environment
variable, that instructs the Skia/FemtoVG renderers to rotate
the scene before rendering.
This doesn't require a windowing system, just Linux and Vulkan drivers
that supports the display extensions.
It's called linuxkms as soon this will go beyond Vulkan and also support
EGL and perhaps dumb buffers for software rendering.
