bmpblk: add veyron_{brain,mickey,romy} as Chromeboxes

BUG=none
BRANCH=none
TEST=built and booted on Brain (with HDMI patches), saw
dev mode screen

Change-Id: I10ea10f4ab0d1fb1fab9afe7b299cee8307bedb5
Reviewed-on: https://chrome-internal-review.googlesource.com/218069
Reviewed-by: Hung-Te Lin <hungte@google.com>
Commit-Queue: David Hendricks <dhendrix@google.com>
Tested-by: David Hendricks <dhendrix@google.com>