docs: Move arm-cpu-features.rst into the system manual

Now we have somewhere to put arm-specific rst documentation,
we can move arm-cpu-features.rst from the docs/ top level
directory into docs/system/arm/.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-id: 20200309215818.2021-5-peter.maydell@linaro.org
2 files changed