Add two new opcodes that userspace can use for admin commands:
NVME_URING_CMD_ADMIN : non-vectroed
NVME_URING_CMD_ADMIN_VEC : vectored variant

Wire up support when these are issued on controller node(/dev/nvmeX).
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220520090630.70394-3-joshi.k@samsung.comSigned-off-by: Jens Axboe <axboe@kernel.dk>