From: Suanming Mou <redacted>

A keytag is a piece of data encrypted together with a DEK.

When a DEK is referenced by an MKEY.bsf through its index, the keytag is
also supplied in the BSF as plaintext. The HW will decrypt the DEK (and
the attached keytag) and will fail the operation if the keytags don't
match.

This commit adds the configuration of the keytag with devargs.

Signed-off-by: Suanming Mou <redacted>
Signed-off-by: Matan Azrad <redacted>
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Documentation for devargs should be part of this patch.
Please split the last patch accordingly.

Title can be shortened to
Crypto/mlx5: add keytag devarg

Fix other patches of devargs accordingly.