rockchip: dts: rk3399-puma: Add DDR3-1600 timings and use for Puma

With the validation done for DDR3-1600 (i.e. 800 MHz bus clock), we
add the timings (rk3399-sdram-ddr3-1600.dtsi) and change rk3399-puma.dts
to use these by default.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Simon Glass <sjg@chromium.org>
Drop blank line at end of file:
Signed-off-by: Simon Glass <sjg@chromium.org>