vb21: Rename struct vb2_guid to struct vb2_id

Since the ID structure isn't a true GUID anymore, let's call it
something else.

BUG=none
BRANCH=none
TEST=make runtests

Change-Id: I96f511bd5587a94d2cc20764e26d7ef0096de04c
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/256182
Reviewed-by: Randall Spangler <rspangler@chromium.org>
22 files changed