doc: update Kernel documentation build system

Update the documentation build system according to Linux v5.11-rc1.

Deactive the automarkup.py extension module which on Gitlab CI is
incompatible with Unicode.

With this patch we can build the HTML documentation using either of
Sphinx 2 and Sphinx 3.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/sphinx/parse-headers.pl b/doc/sphinx/parse-headers.pl
index c518050..b063f2f 100755
--- a/doc/sphinx/parse-headers.pl
+++ b/doc/sphinx/parse-headers.pl
@@ -1,4 +1,4 @@
-#!/usr/bin/perl
+#!/usr/bin/env perl
 use strict;
 use Text::Tabs;
 use Getopt::Long;
@@ -110,7 +110,7 @@
 	    ) {
 		my $s = $1;
 
-		$structs{$s} = "struct :c:type:`$s`\\ ";
+		$structs{$s} = "struct $s\\ ";
 		next;
 	}
 }
@@ -393,7 +393,7 @@
 
 Copyright (c) 2016 by Mauro Carvalho Chehab <mchehab+samsung@kernel.org>.
 
-License GPLv2: GNU GPL version 2 <http://gnu.org/licenses/gpl.html>.
+License GPLv2: GNU GPL version 2 <https://gnu.org/licenses/gpl.html>.
 
 This is free software: you are free to change and redistribute it.
 There is NO WARRANTY, to the extent permitted by law.