lpfc: Refactor nvmet_rcv_ctx to create lpfc_async_xchg_ctx

To support FC-NVME-2 support (actually FC-NVME (rev 1) with Ammendment 1),
both the nvme (host) and nvmet (controller/target) sides will need to be
able to receive LS requests.  Currently, this support is in the nvmet side
only. To prepare for both sides supporting LS receive, rename
lpfc_nvmet_rcv_ctx to lpfc_async_xchg_ctx and commonize the definition.

Signed-off-by: Paul Ely <paul.ely@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>