android: base-cfg: enable DM_VERITY (used for secureboot)

Change-Id: I68d769f97ffa76bb45e65d34a96dd7f558c02d08
Signed-off-by: JP Abgrall <jpa@google.com>
(cherry picked from commit 37cb5bec8983e505eecb730188bfc113d087dee7)