arm64: dts: imx8ulp: drop undocumented property in cgc

The clocks and clocks-names are not documented in binding doc,
and the clk-imx8ulp driver not use the undocumented property,
so drop them.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>