doc: add structure to Sphinx generated docs

Create separate html pages for linker lists, the serial subsystem,
and the EFI subsystem.

Add a table of content.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/Documentation/serial.rst b/Documentation/serial.rst
new file mode 100644
index 0000000..ed34e59
--- /dev/null
+++ b/Documentation/serial.rst
@@ -0,0 +1,7 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Serial system
+=============
+
+.. kernel-doc:: drivers/serial/serial.c
+   :internal: