config: add backup coreboot submodule repositories

this is using the same functionality that was added a few
commits ago, to override the use of "git submodule update"

each coreboot submodule has two repositories defined, with
the second one kicking in if the mail one fails upon cloning.

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/submodule/coreboot/fam15h_rdimm/vboot/module.cfg

@@ -0,0 +1,3 @@
+subrepo="https://review.coreboot.org/vboot.git"
+subrepo_bkup="https://github.com/coreboot/vboot"
+subrev="ecdca931ae0637d1a9498f64862939bd5bb99e0b"

config/submodule/coreboot/fam15h_rdimm/vboot/patches/0001-don-t-treat-warnings-as-errors.patch

@@ -1,6 +1,6 @@
-From ba16c0fe8236bd511e879693527993ce8ce3668b Mon Sep 17 00:00:00 2001
+From 2c5c8d9a5c999a5eedd9f17acb0bd3924524657d Mon Sep 17 00:00:00 2001
 From: Leah Rowe <info@minifree.org>
-Date: Tue, 21 May 2024 23:19:38 +0100
+Date: Tue, 21 May 2024 23:21:14 +0100
 Subject: [PATCH 1/1] don't treat warnings as errors
 
 Signed-off-by: Leah Rowe <info@minifree.org>