mb/google/poppy: Add variant for Atlas

Add a new variant of Poppy for the Atlas board.

TEST=tested on a P0 board.  System boots and is mostly
functional, though some peripherals are not ready so there
are no touchpad/touchscreen devices configured yet.

Change-Id: I5a0bccd1bda0134aa51885ac2c6e7bb5b45de924
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/25389
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
10 files changed