dt-bindings: fsl: scu: add imx8dxl scu clock support

Add imx8dxl scu clock support.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20220222082140.2073629-1-abel.vesa@nxp.com