doc: shorten overlong title underlines

Title underlines should match the length of the title. Unfortunately
docutils only catches underlines that are too short.

Add some missing empty lines after titles.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/board/AndesTech/ae350.rst b/doc/board/AndesTech/ae350.rst
index 42a2b4d..99622fd 100644
--- a/doc/board/AndesTech/ae350.rst
+++ b/doc/board/AndesTech/ae350.rst
@@ -1,7 +1,7 @@
 .. SPDX-License-Identifier: GPL-2.0+
 
 AE350
-======
+=====
 
 AE350 is the mainline SoC produced by Andes Technology using AndesV5 CPU core
 based on RISC-V architecture.