In host mode, the host is expected to send HPB WRITE BUFFER with buffer-id
= 0x1 when it inactivates a region.

Use the map-requests pool as there is no point in assigning a designated
cache for umap-requests.

[mkp: REQ_OP_DRV_*]

Link: https://lore.kernel.org/r/20210712095039.8093-7-avri.altman@wdc.comReviewed-by: Daejun Park <daejun7.park@samsung.com>
Signed-off-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>