usb: dwc2: Disable clock gating feature on Rockchip SoCs

The DWC2 IP on the Rockchip SoCs doesn't support clock gating.
When a clock gating is enabled, system hangs.

Signed-off-by: William Wu <william.wu@rock-chips.com>
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Link: https://lore.kernel.org/r/1703575199-23638-1-git-send-email-william.wu@rock-chips.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>