nvme: don't query identify data in configure_metadata

Move reading the Identify Namespace Data Structure, NVM Command Set out
of configure_metadata into the caller.  This allows doing the identify
call outside the frozen I/O queues, and prepares for using data from
the Identify data structure for other purposes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>