nvme: implement log page low/high offset and dwords

NVMe 1.2.1 extends the get log page interface to include 64 bit
offset and increases the number of dwords to 32 bits. Implement
for future use.

Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>