arm64: dts: rockchip: Add dma-names to uart-bluetooth rk3566 devices

[Diederik de Haas]

This is a single patch which adds the dma-names property to the uart
node with a bluetooth subnode on Pine64's rk356x devices.

But that property can potentially be added to several other devices, but
I have zero familiarity with them or their community, so I choose not to
add it to those devices, but inform people via this cover letter.

The dts/dtsi files I found as potential candidates are:
- rk3566-anbernic-rgxx3.dtsi
- rk3566-box-demo.dts
- rk3566-powkiddy-rk2023.dtsi
- rk3566-powkiddy-x55.dts
- rk3566-radxa-cm3.dtsi
- rk3566-rock-3c.dts
- rk3566-roc-pc.dts
- rk3568-rock-3a.dts