Revert "Remove Gru platform"

This reverts commit d6c45f445712bbf36b58f5b1e9d1c588e461dd56.

We need 'gru' so that we can build 'scarlet' as part of
http://go/cros-unmonitored-builds

BUG=b:321067912
TEST=build and deploy a scarlet build to a dru

Change-Id: I3fcc5ee622425fa8368828e342eda3e74bb023ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/mosys/+/5318541
Reviewed-by: Jack Rosenthal <[email protected]>
Tested-by: Ross Zwisler <[email protected]>
Commit-Queue: Ross Zwisler <[email protected]>
Auto-Submit: Ross Zwisler <[email protected]>
4 files changed