bhyve: fix NVMe Get Features, Predictable Latency

If the Predictable Latency Mode is not supported, NVMe Controllers must
return Invalid Field in Command status for the Get Features command
with IDs:

• Predictable Latency Mode Config
• Predictable Latency Mode Window

Fixes UNH Tests 3.6

Tested by: Jason Tubnor
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D24899