drm/debugfs: drop debugfs_init() for the render and accel node v2

We want to remove per minor debugfs directories. Start by stopping
drivers from adding anything inside of those in the mid layer callback.

v2: drop it for the accel node as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Tested-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230829110115.3442-2-christian.koenig@amd.com