The TCG mandates two Key derivation functions called KDFa and KDFe
used to derive keys from seeds and elliptic curve points respectively.
The definitions for these functions are found in the TPM 2.0 Library
Specification Part 1 - Architecture Guide

https://trustedcomputinggroup.org/resource/tpm-library-specification/

Implement a cut down version of each of these functions sufficient to
support the key derivation needs of HMAC sessions.
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>