11608 add DKIOC ioctl to report drive UNMAP support
Review Request #2263 - Created Aug. 26, 2019 and submitted
This is a new ioctl which can be used to determine if a device supports UNMAP. This will be consumed by the port from ZoL of the TRIM code.
Tested with a small program which issues the ioctl to a device and reports the result. Ran against a regular disk which reports false, and a trimmable SSD which reports true.