Update vboot submodule to upstream main

Updating from commit id ecb87bfc:
    Add PRESUBMIT.py

to commit id 03c8969b:
    get_gbb_flags.sh: Use futility gbb --explicit

This brings in 23 new commits.

Change-Id: Ie5a20071f00e61e03193eef79b3b123cf25fe4e0
Signed-off-by: Yidi Lin <yidilin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72944
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

3rdparty/vboot

@@ -1 +1 @@
-Subproject commit a09b792e6a159d7d21b8e64f07a056ba08f8014d
+Subproject commit 03c8969b86187ac1a0dd93a5de5e4b60a0531783