google/edgar: add new board as variant of cyan baseboard

Add support for google/edgar (Acer Chromebook 14 CB3-431) as
a variant of the cyan Braswell basebaseboard.

- Add board-specific code as the new edgar variant
- Add common code to the baseboard which will apply to all
  variants other than cyan

Sourced from Chromium branch firmware-edgar-7287.167.B,
commit 2319742: Edgar: Add Micron MT52L256M32D1PF-107 SPD data

Change-Id: I58548cbbc85828f37c0023e8aa9e09bdca612659
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/21127
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
19 files changed