Documentation: Update paths of Samsung S3C machine files

Documentation references Samsung S3C24xx and S3C64xx machine files in
multiple places but the files were traveling around the kernel multiple
times.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200911143343.498-1-krzk@kernel.org