imsm: Change the way of printing nvme drives in detail-platform.

imsm: Change the way of printing nvme drives in detail-platform.

Change NVMe controller path to device node path
in mdadm --detail-platform and print serial number.
The method imsm_read_serial always trimes serial to
MAX_RAID_SERIAL_LEN, added parameter 'serial_buf_len'
will be used to check the serial fit
to passed buffor, if not, will be trimed.

Signed-off-by: Blazej Kucman <blazej.kucman@intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>