ARM: dts: da850: add the mstpri and ddrctl nodes

Add the nodes for the MSTPRI configuration and DDR2/mDDR memory
controller drivers to da850.dtsi.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>