openrisc: dts: Add de0 nano multicore config and devicetree

openrisc: dts: Add de0 nano multicore config and devicetree

Add a multicore configuration for the Terasic de0 nano FPGA development
board.  This SoC runs 2 OpenRISC CPUs at 50Mhz with 32MB ram, UART for
console and GPIOs for LEDs.

This FPGA SoC is based on the simple-smp reference board and brings in
devices from the de0 nano common DTSI file.

A default config is added that brings together the device tree and
driver setup.

Link: https://github.com/stffrdhrn/de0_nano-multicore
Signed-off-by: Stafford Horne <shorne@gmail.com>