UPSTREAM: docs/releases/4.21: Add toolchain updates

(cherry picked from commit 7473671b8bbad420e04e8843b309d51b1a941db9)

Original-Change-Id: Ibd7c23a8c7c30ff19e0564d01489fecb3f34dadc
Original-Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Original-Reviewed-on: https://review.coreboot.org/c/coreboot/+/75414
Original-Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Original-Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
GitOrigin-RevId: 7473671b8bbad420e04e8843b309d51b1a941db9
Change-Id: I949f6ea37ed476c76debd2488d46121b3b3febaa
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/coreboot/+/4573425
Commit-Queue: Nick Vaccaro <nvaccaro@google.com>
Tested-by: CopyBot Service Account <copybot.service@gmail.com>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
diff --git a/Documentation/releases/coreboot-4.21-relnotes.md b/Documentation/releases/coreboot-4.21-relnotes.md
index 2e4131a..8c34dcb 100644
--- a/Documentation/releases/coreboot-4.21-relnotes.md
+++ b/Documentation/releases/coreboot-4.21-relnotes.md
@@ -20,6 +20,11 @@
 * This section should have full descriptions and can or should have
   a link to the referenced commits.
 
+### Toolchain updates
+
+* Upgrade IASL from 20221020 to 20230331
+* Upgrade LLVM from 15.0.7 to 16.0.4
+
 Additional coreboot changes
 ---------------------------