KEYS: trusted: Introduce NXP DCP-backed trusted keys

DCP (Data Co-Processor) is the little brother of NXP's CAAM IP.
Beside of accelerated crypto operations, it also offers support for
hardware-bound keys. Using this feature it is possible to implement a blob
mechanism similar to what CAAM offers. Unlike on CAAM, constructing and
parsing the blob has to happen in software (i.e. the kernel).

The software-based blob format used by DCP trusted keys encrypts
the payload using AES-128-GCM with a freshly generated random key and nonce.
The random key itself is AES-128-ECB encrypted using the DCP unique
or OTP key.

The DCP trusted key blob format is:
/*
 * struct dcp_blob_fmt - DCP BLOB format.
 *
 * @fmt_version: Format version, currently being %1
 * @blob_key: Random AES 128 key which is used to encrypt @payload,
 *            @blob_key itself is encrypted with OTP or UNIQUE device key in
 *            AES-128-ECB mode by DCP.
 * @nonce: Random nonce used for @payload encryption.
 * @payload_len: Length of t...