drm/doc: Clarify what ioctls can be used on render nodes

The documentation for render nodes indicates that only "PRIME-related"
ioctls are valid on render nodes, but the documentation does not clarify
what that means.  If the reader is not familiar with PRIME, they may
beleive this to be only the ioctls with "PRIME" in the name and not other
ioctls such as set of syncobj ioctls.  Clarify the situation for the
reader by referencing where the reader will find a current list of valid
ioctls.
Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1646667156-16366-1-git-send-email-quic_jhugo@quicinc.com

Documentation/gpu/drm-uapi.rst

@@ -148,7 +148,9 @@ clients together with the legacy drmAuth authentication procedure.
 If a driver advertises render node support, DRM core will create a
 separate render node called renderD<num>. There will be one render node
 per device. No ioctls except PRIME-related ioctls will be allowed on
-this node. Especially GEM_OPEN will be explicitly prohibited. Render
+this node. Especially GEM_OPEN will be explicitly prohibited. For a
+complete list of driver-independent ioctls that can be used on render
+nodes, see the ioctls marked DRM_RENDER_ALLOW in drm_ioctl.c  Render
 nodes are designed to avoid the buffer-leaks, which occur if clients
 guess the flink names or mmap offsets on the legacy interface.
 Additionally to this basic interface, drivers must mark their