Patch merged into coreboot/master: lib/boot_device: add RW boot device construct

the following patch was just integrated into master:
commit dcbccd6a1ef1ee70d6e96f01c55c8ed270f37716
Author: Aaron Durbin 
Date:   Wed Aug 10 11:42:42 2016 -0500

lib/boot_device: add RW boot device construct

The current boot device usage assumes read-only semantics to
    the boot device. Any time someone wants to write to the
    boot device a device-specific API is invoked such as SPI flash.
    Instead, provide a mechanism to retrieve an object that can
    be used to perform writes to the boot device. On systems where
    the implementations are symmetric these devices can be treated
    one-in-the-same. However, for x86 systems with memory mapped SPI
    the read-only boot device provides different operations.

BUG=chrome-os-partner:55932

Change-Id: I0af324824f9e1a8e897c2453c36e865b59c4e004
    Signed-off-by: Aaron Durbin 
    Reviewed-on: https://review.coreboot.org/16194
    Tested-by: build bot (Jenkins)
    Reviewed-by: Furquan Shaikh 
    Reviewed-by: Paul Menzel

See https://review.coreboot.org/16194 for details.

-gerrit