google/gru: Read RAM & board ids from the ADC

- Update so that the RAM id is read from ADC instead of
hard-coded from the config array.
- Update the boardid readings so that they are bucketed instead
of within an error margin.

BRANCH=None
BUG=chrome-os-partner:54566,chrome-os-partner:53988
TEST=hexdump /proc/device-tree/firmware/coreboot/ram-code
     and boardid when OS boots up.  Also verified that
     voltage read in debug output returns correct id.

Change-Id: I963406d8c440cd90c3024c814c0de61d35ebe2fd
Signed-off-by: Martin Roth <martinroth@chromium.org>
Original-Commit-Id: 068705a38734d2604f71c8a7b5bf2cc15b0f7045
Original-Change-Id: I1c847558d54a0f7f9427904eeda853074ebb0e2e
Original-Signed-off-by: Shelley Chen <shchen@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/356584
Original-Reviewed-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: https://review.coreboot.org/15586
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
2 files changed