util: Introduce md_get_array_info()

util: Introduce md_get_array_info()

Remove most direct ioctl calls for GET_ARRAY_INFO, except for one,
which will be addressed in the next patch.

This is the start of the effort to clean up the use of ioctl calls and
introduce a more structured API, which will use sysfs and fall back to
ioctl for backup.

Signed-off-by: Jes Sorensen <Jes.Sorensen@gmail.com>