gpio: Remove non-ternary tristate mode, make ternaries easier

The function to read board IDs from tristate GPIOs currently supports
two output modes: a normal base-3 integer, or a custom format where
every two bits represent one tristate pin. Each board decides which
representation to use on its own, which is inconsistent and provides
another possible gotcha to trip over when reading unfamiliar code.

The two-bits-per-pin format creates the additional problem that a
complete list of IDs (such as some boards use to build board-ID tables)
necessarily has "holes" in them (since 0b11 does not correspond to a
possible pin state), which makes them extremely tricky to write, read
and expand. It's also very unintuitive in my opinion, although it was
intended to make it easier to read individual pin states from a hex
representation.

This patch switches all boards over to base-3 and removes the other
format to improve consistency. The tristate reading function will just
print the pin states as they are read to make it easier to debug them,
and we add a new BASE3() macro that can generate ternary numbers from
pin states. Also change the order of all static initializers of board ID
pin lists to write the most significant bit first, hoping that this can
help clear up confusion about the endianness of the pins.

CQ-DEPEND=CL:219902
BUG=None
TEST=Booted on a Nyan_Blaze (with board ID 1, unfortunately the only one
I have). Compiled on Daisy, Peach_Pit, Nyan, Nyan_Big, Nyan_Blaze, Rush,
Rush_Ryu, Storm, Veryon_Pinky and Falco for good measure.

Change-Id: I3ce5a0829f260db7d7df77e6788c2c6d13901b8f
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 2fa9545ac431c9af111ee4444d593ee4cf49554d
Original-Change-Id: I6133cdaf01ed6590ae07e88d9e85a33dc013211a
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/219901
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9401
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

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