ARM: dts: rockchip: move oscillator input clock into main dtsi

The clock definitions get a lot shorter due to the soc clocks being handled by
rk3188-cru and only the input clock remains. These can now simply live
in the main rk3xxx.dtsi without affecting readability.

At the same time, rename the node to oscillator, adding a clock-output-names
property to match how the rk3288 handles this.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-By: Max Schwarz <max.schwarz@online.de>
Tested-By: Max Schwarz <max.schwarz@online.de>