pclk_xpcs is not supported by mainline driver and breaks dtbs_check

following warnings occour, and many more

rk3568-evb1-v10.dt.yaml: ethernet@fe2a0000: clocks:
    [[15, 386], [15, 389], [15, 389], [15, 184], [15, 180], [15, 181],
    [15, 389], [15, 185], [15, 172]] is too long
	From schema: Documentation/devicetree/bindings/net/snps,dwmac.yaml
rk3568-evb1-v10.dt.yaml: ethernet@fe2a0000: clock-names:
    ['stmmaceth', 'mac_clk_rx', 'mac_clk_tx', 'clk_mac_refout', 'aclk_mac',
    'pclk_mac', 'clk_mac_speed', 'ptp_ref', 'pclk_xpcs'] is too long
	From schema: Documentation/devicetree/bindings/net/snps,dwmac.yaml

after removing it, the clock and other warnings are gone.

pclk_xpcs on gmac is used to support QSGMII, but this requires a driver
supporting it.
Once xpcs support is introduced, the clock can be added to the
documentation and both controllers.

Fixes: b8d41e50 ("arm64: dts: rockchip: add gmac0 node to rk3568")
Co-developed-by: Peter Geis <pgwipeout@gmail.com>
Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Acked-by: Michael Riesch <michael.riesch@wolfvision.net>
Link: https://lore.kernel.org/r/20220123133510.135651-1-linux@fw-web.deSigned-off-by: Heiko Stuebner <heiko@sntech.de>