doc: Remove duplicated documentation directory

Commit ad7061ed74 ("doc: Move device tree bindings documentation to
 doc/device-tree-bindings") moved all device tree binding documentation
to doc/device-tree-bindings directory.

The current U-Boot project still have two documentation directories:

- doc/
- Documentation/

Move all documentation and sphinx files to doc directory so all content
can be in a common place.

Signed-off-by: Breno Lima <breno.lima@nxp.com>

doc/sphinx/load_config.py

@@ -0,0 +1,32 @@
+# -*- coding: utf-8; mode: python -*-
+# pylint: disable=R0903, C0330, R0914, R0912, E0401
+
+import os
+import sys
+from sphinx.util.pycompat import execfile_
+
+# ------------------------------------------------------------------------------
+def loadConfig(namespace):
+# ------------------------------------------------------------------------------
+
+    u"""Load an additional configuration file into *namespace*.
+
+    The name of the configuration file is taken from the environment
+    ``SPHINX_CONF``. The external configuration file extends (or overwrites) the
+    configuration values from the origin ``conf.py``.  With this you are able to
+    maintain *build themes*.  """
+
+    config_file = os.environ.get("SPHINX_CONF", None)
+    if (config_file is not None
+        and os.path.normpath(namespace["__file__"]) != os.path.normpath(config_file) ):
+        config_file = os.path.abspath(config_file)
+
+        if os.path.isfile(config_file):
+            sys.stdout.write("load additional sphinx-config: %s\n" % config_file)
+            config = namespace.copy()
+            config['__file__'] = config_file
+            execfile_(config_file, config)
+            del config['__file__']
+            namespace.update(config)
+        else:
+            sys.stderr.write("WARNING: additional sphinx-config not found: %s\n" % config_file)