rockchip: rk3368: improve Kconfig text for the RK3368

rockchip: rk3368: improve Kconfig text for the RK3368

The RK3368 option in Kconfig referred to the RK3328 (copy-and-paste)
and had a few typos and unnecessarily used UTF-8 characters.  While
fixing this, I also reformatted and further clarified the text
(e.g. made the grouping into a a big and little cluster of 4 cores
each explicit).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>