Add PKCS #5 v2.0 key derivation function 2 (PBKDF2)

This commit implements a crypto extension to support the key derivation
function defined in section 5.2 of RFC 2898
(https://www.ietf.org/rfc/rfc2898.txt), which is a re-publish of PKCS #5 v2.0.
The underlying pseudorandom function is HMAC-SHA1, which is the default PRF
specified in the RFC. It would be trivial to support the other HMAC functions
already implemented in OP-TEE.

See documentation/extensions/crypto_pbkdf2.md for details.

Tested on PLATFORM=vexpress-qemu_virt with the test vectors from RFC 6070
(https://www.ietf.org/rfc/rfc6070.txt).

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Xiaoqiang Du <xiaoqiang.du@linaro.org>
The code would keep the last occurrence, which I *thought* was the expected behavior, but I was wrong. GP TEE Internal API specifies that:
> When an array of attributes is passed to a function, either to populate an object or to specify operation parameters, and if an attribute identifier is present twice in the array, then only the first occurrence is used.

I'll fix the code.