arm64: dts: rockchip: Add DFI to rk356x

The DFI unit can be used to measure DRAM utilization using perf. Add the
node to the device tree.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20231018061714.3553817-26-s.hauer@pengutronix.de


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