nvme-pci: expose use_threaded_interrupts read-only in sysfs

Allow reading /sys/module/nvme/parameters/use_threaded_interrupts to see
if the use_threaded_interrupts module parameter is in use.

Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>