Documentation: Fix spelling errors

These issues were found and fixed by codespell, a useful tool for
finding spelling errors.

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: If2a8e97911420c19e9365d5c28810b998f2c2ac8
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58078
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/conf.py

@@ -185,7 +185,7 @@ texinfo_documents = [
 enable_auto_toc_tree = True
 
 class MyCommonMarkParser(CommonMarkParser):
-    # remove this hack once upsteam RecommonMark supports inline code
+    # remove this hack once upstream RecommonMark supports inline code
     def visit_code(self, mdnode):
         from docutils import nodes
         n = nodes.literal(mdnode.literal, mdnode.literal)