Rework kpss-gcc driver Documentation to yaml Documentation and move it
to clock as it's a clock-controller.
The current kpss-gcc Documentation have major problems and can't be
converted directly. Introduce various changes to the original
Documentation.

Add #clock-cells additional binding as this clock outputs a static clk
named acpu_l2_aux with supported compatible.
Only some compatible require and outputs a clock, for the others, set
only the reg as a required binding to correctly export the kpss-gcc
registers. As the reg is shared also add the required syscon compatible.
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230116204751.23045-4-ansuelsmth@gmail.com