dt-bindings: soc: cix: document the syscon on Sky1 SoC

dt-bindings: soc: cix: document the syscon on Sky1 SoC

There are two system control on Cix sky1 Soc. One is located in S0 domain,
and the other is located in S5 domain. The system control contains resets,
usb typeC and more. At this point, only the reset controller is embedded
as usb typeC uses it by phandle.

Signed-off-by: Gary Yang <gary.yang@cixtech.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>