firmware: Add recovery menu support for detachables
firmware: Add recovery menu support for detachables

Adding in basic menu support (using arrow keys) for
detachables.  This is specifically for the recovery menu.

BUG=chrome-os-partner:61275
BRANCH=None
TEST=reboot into recovery and try booting into developer mode.

Change-Id: I9596cde62f2748928b4b796bde0a0226dc981235
Signed-off-by: Shelley Chen <ab7b8cc85923339aed379eb1c5cc4dccfd2eb3d7@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/424354

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot