[PATCH] docs/about/deprecated.rst: Add "since 7.1" tag to dtb-kaslr-seed deprecation

[Peter Maydell <peter.maydell@linaro.org>]

In commit 5242876f37ca we deprecated the dtb-kaslr-seed property of
the virt board, but forgot the "since n.n" tag in the documentation
of this in deprecated.rst.

This deprecation note first appeared in the 7.1 release, so
retrospectively add the correct "since 7.1" annotation to it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
My mistake, since I added the deprecation.rst text to that commit.
---
 docs/about/deprecated.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index 1ca9dc33d61..914938fd76a 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -219,8 +219,8 @@ Use the more generic event ``DEVICE_UNPLUG_GUEST_ERROR`` instead.
 System emulator machines
 ------------------------
 
-Arm ``virt`` machine ``dtb-kaslr-seed`` property
-''''''''''''''''''''''''''''''''''''''''''''''''
+Arm ``virt`` machine ``dtb-kaslr-seed`` property (since 7.1)
+''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 
 The ``dtb-kaslr-seed`` property on the ``virt`` board has been
 deprecated; use the new name ``dtb-randomness`` instead. The new name
-- 
2.34.1