Honor the FWUG value of some drives in nvmecontrol

nvmecontrol tries to upload firmware in chunks as large as it thinks
the device permits. It fails to take into account the FWUG value used
by some drives to advertise the size and alignment limits for firmware
chunks.

• Use the firwmare update granularity value from the
• If the granularity is not reported or not restricted, fall back to the previously existing logic that calculates the max transfer size based on MDTS.
• Add firmware update granularity to the identify-controller output.

Reviewed by: imp (previous version), chuck
Obtained from: Dell EMC Isilon
MFC after: 1 week
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D26390