Add support for SHA-based KDFs for ECDH

[beamer159]

PKCS11 defines the following EC KDFs:

• CKD_NULL
• CKD_SHA1_KDF
• CKD_SHA224_KDF
• CKD_SHA256_KDF
• CKD_SHA384_KDF
• CKD_SHA512_KDF

It looks like the only currently supported KDF is CKD_NULL:

rust-cryptoki/cryptoki/src/mechanism/elliptic_curve.rs

Lines 46 to 51 in 617efa8

	impl EcKdfType {
	/// The null transformation. The derived key value is produced by
	/// taking bytes from the left of the agreed value. The new key
	/// size is limited to the size of the agreed value.
	pub const NULL: EcKdfType = EcKdfType { val: CKD_NULL };
	}

[ionut-arm]

Hey! Thanks for the request - any chance you'd be up to contribute those?

[hug-dev]

#239 does it for SHA256. It's not all you posted first but I guess we can close it after that, and re-open if more are still needed :)