dt-bindings: add documentation for rk3188 clock and reset unit

This add bindings documentation for the clock and reset unit found on
rk3188 and rk3066 SoCs from Rockchip.

Also deprecate the old gate clock binding, as these shouldn't be used
in the future.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-By: Max Schwarz <max.schwarz@online.de>
Tested-By: Max Schwarz <max.schwarz@online.de>
Signed-off-by: Mike Turquette <mturquette@linaro.org>