The DFI unit can be used to measure DRAM utilization using perf. Add the
node to the device tree. The DFI needs a rockchip,pmu phandle to the pmu
containing registers for SDRAM configuration details. This is added in
this patch as well.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>