docs: staging: fix typo in docs

Resolve a spelling error in the documentation found
with codespell.

Signed-off-by: Vincenzo Mezzela <vincenzo.mezzela@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240208162748.111120-1-vincenzo.mezzela@gmail.com

doc: rmpsg: Update with rpmsg_endpoint

It seems the documentation was not updated when `rpmsg_sendto`
and related switched from `rpmsg_channel` to `rpmsg_endpoint`.
This change updates the proper calls, text, and the sample.

Signed-off-by: Adrien Leravat <adrien.leravat@gmail.com>
Link: https://lore.kernel.org/r/20231203200606.255302-1-adrien.leravat@gmail.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

docs: move remaining stuff under Documentation/*.txt to Documentation/staging

There are several files that I was unable to find a proper place
for them, and 3 ones that are still in plain old text format.

Let's place those stuff behind the carpet, as we'd like to keep the
root directory clean.

We can later discuss and move those into better places.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/11bd0d75e65a874f7c276a0aeab0fe13f3376f5f.1592203650.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>