docs: acpi: fix old http link and improve document format

The website:

    http://wiki.minnowboard.org

doesn't exist anymore. The same pages are moved to:

    https://www.elinux.org/Minnowboard

Other improvements concern the introduction of some rst
semantic markup in the document.
Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Link: https://lore.kernel.org/r/20200519084128.12756-2-f.suligoi@asem.itSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/acpi/ssdt-overlays.rst

@@ -63,7 +63,7 @@ which can then be compiled to AML binary format::
     ASL Input:     minnomax.asl - 30 lines, 614 bytes, 7 keywords
     AML Output:    minnowmax.aml - 165 bytes, 6 named objects, 1 executable opcodes
 
-[1] http://wiki.minnowboard.org/MinnowBoard_MAX#Low_Speed_Expansion_Connector_.28Top.29
+[1] https://www.elinux.org/Minnowboard:MinnowMax#Low_Speed_Expansion_.28Top.29
 
 The resulting AML code can then be loaded by the kernel using one of the methods
 below.