drm: document minimum kernel version for DRM_CLIENT_CAP_*

drm: document minimum kernel version for DRM_CLIENT_CAP_*

The kernel versions including the following commits are referenced:

DRM_CLIENT_CAP_STEREO_3D
5e3af27819f9 ("drm: Add a STEREO_3D capability to the SET_CLIENT_CAP ioctl")

DRM_CLIENT_CAP_UNIVERSAL_PLANES
5d5c46bd9025 ("drm: Allow userspace to ask for universal plane list (v2)")
1e549de6f0cd ("drm: Remove command line guard for universal planes")

DRM_CLIENT_CAP_ATOMIC
66944525c1f9 ("drm: add atomic properties")
35390efa4a1c ("drm: Always enable atomic API")

DRM_CLIENT_CAP_ASPECT_RATIO
cbd461a2c173 ("drm: Add DRM client cap for aspect-ratio")

DRM_CLIENT_CAP_WRITEBACK_CONNECTORS
56eae8a3375e ("drm: writeback: Add client capability for exposing writeback connectors")

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Daniel Stone <daniels@collabora.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/434202/