Patch merged into coreboot/master: gpio: Add support for binary_first base3 number system

the following patch was just integrated into master:
commit 2b239485358ec063a4803f248c88378076810e24
Author: Julius Werner 
Date:   Wed Mar 16 17:11:55 2016 -0700

gpio: Add support for binary_first base3 number system

This patch adds support for an alternative ternary number system in
    which group of GPIOs can be interpreted. In this system, the digit
    combinations that would form a binary number (i.e. that contain no 'Z'
    state) are used to represent the lower values in the way they're used in
    the normal binary system, and all the combinations that do contain a 'Z'
    are used to represent values above those. We can use this for boards
    that originally get strapped with binary board IDs but eventually
    require more revisions than that representation allows. We can switch
    their code to binary_first base3 and all old revisions with already
    produced boards will still get read as the correct numbers.

Credit for the algorithm idea goes to Haran Talmon.

BRANCH=None
    BUG=None
    TEST=Stubbed out the actual GPIO reading and simulated all combinations
    of 4 ternary digits for both number systems.

Change-Id: Ib5127656455f97f890ce2999ba5ac5f58a20cf93
    Signed-off-by: Julius Werner 
    Reviewed-on: https://review.coreboot.org/14116
    Tested-by: build bot (Jenkins)
    Reviewed-by: David Hendricks 
    Reviewed-by: Aaron Durbin

See https://review.coreboot.org/14116 for details.

-gerrit