nvme: improve NVME_HOST_AUTH and NVME_TARGET_AUTH config descriptions

Currently two similar config options NVME_HOST_AUTH and NVME_TARGET_AUTH
have almost same descriptions. It is confusing to choose them in
menuconfig. Improve the descriptions to distinguish them.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>