vboot: move to region_devices

Now that vboot is using offsets for everything remove the
pass through vboot_get_region() and use region_devices
as first class citizens.

Change-Id: I1a86f3725e5bce38e6ca31e9641b1a8f4ac50e96
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10225
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
7 files changed