drm: Stop using an embedded struct drm_device in driver softcs
* All drm drivers use a struct drm_device record but are free to
allocate it by themselves in different ways or let the generic
drm subsystem code do it.
* This drm_device record can even be part of another data structure,
dynamically or statically allocated.
* We cannot just assume the length of a drm_device structure in the
softc memory block will be enough to store all driver private data.
* Make the drm softc the equivalent of a void* pointer and let the
upstream code behave as expected on Linux
UnifiedSplitRaw
