[PATCH v3] nvme: enable FDP support

[Keith Busch]

I like concensus on features, but I don't think we're going to get that
here. It's my opinion that FDP is just arbitrary hints, and this is just
one way to map it to other hints. Not a perfect match, but I don't think
it needs to be. It is not realistic for protocols to target a specific
operating system, and Linux's write hints are not exactly a shining
example of an interface for this purpose either.

My first concern for applying something like this is what kind of
maintenance burdens does this create, or any potential harm to users who
don't subscribe to the feature? Nothing here looks alarming to me, and
there is a clear demand to be able to access these features like this.
Maybe it works out for some workloads, maybe it doesn't, but I don't see
a need to block this at this point.