Patch merged into coreboot/master: riscv: add the lowrisc/nexys4ddr mainboard

the following patch was just integrated into master:
commit 66bea528cfde9dea3d84ca571b7cca94964850c4
Author: Ronald G. Minnich 
Date:   Tue Oct 25 19:11:07 2016 -0700

riscv: add the lowrisc/nexys4ddr mainboard

This was tested at the coreboot meeting in Berlin.

The uart programming may still not be right but when used with
    the lowrisc bitstream for the board we were able to load
    and start linux, although it does not yet get far due to
    PTE version issues with lowrisc.

Change-Id: Ia1de1a92762631c9d7bb3d41b04f95296144caa3
    Signed-off-by: Ronald G. Minnich 
    Reviewed-on: https://review.coreboot.org/17132
    Reviewed-by: Aaron Durbin 
    Tested-by: build bot (Jenkins)

See https://review.coreboot.org/17132 for details.

-gerrit