Doc/mainboard: Sort Lenovo laptop generation groups

GM45 is older than Arrandale, so swap their order.

Change-Id: I5b94d940c0378dd561535257d3352700fd482527
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48603
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Evgeny Zinoviev <me@ch1p.io>
diff --git a/Documentation/mainboard/index.md b/Documentation/mainboard/index.md
index 4b46b7c..95efe55 100644
--- a/Documentation/mainboard/index.md
+++ b/Documentation/mainboard/index.md
@@ -89,15 +89,15 @@
 - [X2xx common](lenovo/x2xx_series.md)
 - [vboot](lenovo/vboot.md)
 
-### Arrandale series
-
-- [T410](lenovo/t410.md)
-
 ### GM45 series
 
 - [X200 / T400 / T500 / X301 common](lenovo/montevina_series.md)
 - [X301](lenovo/x301.md)
 
+### Arrandale series
+
+- [T410](lenovo/t410.md)
+
 ### Sandy Bridge series
 
 - [T420](lenovo/t420.md)