arm64: dts: rockchip: use gated-fixed-clock for pcie-refclk on rk3588-tiger

arm64: dts: rockchip: use gated-fixed-clock for pcie-refclk on rk3588-tiger

Using a combination of fixed clock and gpio-gate clock works but does
not describe the actual hardware. Use the gated-fixed-clock binding
to describe this in a nicer way.

Signed-off-by: Heiko Stuebner <heiko.stuebner@cherry.de>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Link: https://patch.msgid.link/20260210080303.680403-3-heiko@sntech.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>