Assemble: don't assemble IMSM array without OROM.

Assemble: don't assemble IMSM array without OROM.

If someone has an IMSM array, and disables RAID in the BIOS
and uses the devices for some other purpose, then they really don't
want mdadm to start syncing the array.

So don't assemble if OROM doesn't confirm it is OK.

There can still be problems for crash-dump not being able to find
the OROM.   Some explicit work-around might be needed for that
rather than a more general workaround that can corrupt data.

Signed-off-by: NeilBrown <neilb@suse.com>