Add blake2 init with key

[coderofstuff]

Description

Blake2 has been added back with this PR #230 by @tjoly-ledger.

There are only 2 init available: one with no parameters and one with parameters {salt, perso}

Please implement the third possible initialization which is with using a key. Something like:

static cx_err_t cx_blake2b_init3_no_throw(cx_blake2b_t* hash,
                                          size_t size,
                                          uint8_t* key,
                                          size_t key_len) {
    if (key == NULL && key_len != 0) {
        goto err;
    }

    if (size % 8 != 0 || size < 8 || size > 512) {
        goto err;
    }
    memset(hash, 0, sizeof(cx_blake2b_t));

    size = size / 8;
    hash->output_size = size;
    hash->header.info = &cx_blake2b_info;

    if (blake2b_init_key(&hash->ctx, size, key, key_len) < 0) {
        goto err;
    }
    return CX_OK;

err:
    return CX_INVALID_PARAMETER;
}

Your environment

• Linux
• branch that causes this issue
• Device (All devices)

[coderofstuff]

@tjoly-ledger have you had the chance to take a look at this? It seems like a logical thing to add to complete support for blake2b