mdadm: Add functions for spare criteria verification

mdadm: Add functions for spare criteria verification

It is done similar way in few places. As a result, two almost identical
functions (dev_size_from_id() and dev_sector_size_from_id()) are
removed. Now, it uses same file descriptor to send two ioctls.

Two extern functions are added, in next patches
disk_fd_matches_criteria() is used.

Next optimization is inline zeroing struct spare_criteria. With that,
we don't need to reset values in get_spare_criteria_imsm().

Dedicated boolean field for checking if criteria are filled is added.
We don't need to execute the code if it is not set.

Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>