docs: kdoc_item: add support to generate a KdocItem from a dict

docs: kdoc_item: add support to generate a KdocItem from a dict

When reading the contents on a KdocItem using YAML, the data
will be imported into a dict.

Add a method to create a new KdocItem from a dict to allow
converting such input into a real KdocItem.

While here, address an issue that, if the class is initialized
with an internal parameter outside the 4 initial arguments,
it would end being added inside other_stuff, which breaks
initializing it from a dict.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <fafeac23d1577927e1a3c32cddfbec1e0209ac73.1773823995.git.mchehab+huawei@kernel.org>