drm/blend: Define the direction of Z position values

We forgot that.

Proof is the one igt testcase we have:

https://gitlab.freedesktop.org/drm/igt-gpu-tools/blob/master/tests/kms_atomic.c#L280

While at it also document that we have immutable zpos properties in
some cases.

Reported-by: Pekka Paalanen <[email protected]>
Cc: Pekka Paalanen <[email protected]>
Reviewed-by: Pekka Paalanen <[email protected]>
Cc: Ilia Mirkin <[email protected]>
Acked-by: Ilia Mirkin <[email protected]>
Reviewed-by: Daniel Stone <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

0 files changed, 0 insertions, 0 deletions