docs: fix RTD build

- Bump python version used when building documentation.
- `setuptools` is a deprecated installation method on RTD so switch to `pip`.
- Add additional dependency on devlib master branch as RTD env is not
  respecting dependency_links during installation.
- Bump copyright year.

doc/requirements.txt

@@ -4,3 +4,4 @@ pandas
 sphinx_rtd_theme==1.0.0
 sphinx==4.2
 docutils<0.18
+devlib @ git+https://github.com/ARM-software/devlib@master

doc/source/conf.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Copyright 2018 ARM Limited
+# Copyright 2023 ARM Limited
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
@@ -68,7 +68,7 @@ master_doc = 'index'
 
 # General information about the project.
 project = u'wa'
-copyright = u'2018, ARM Limited'
+copyright = u'2023, ARM Limited'
 author = u'ARM Limited'
 
 # The version info for the project you're documenting, acts as replacement for