arm64: dts: rockchip: Add support of external clock to ethernet node on Rock 3A SBC

Add support of external clock gmac1_clkin which is used as input clock
to ethernet node.

Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Michael Riesch <michael.riesch@wolfvision.net>
Tested-by: Michael Riesch <michael.riesch@wolfvision.net>
Link: https://lore.kernel.org/r/20221116200150.4657-3-linux.amoon@gmail.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>