überXMHF (rpi3-armv8_32): Support for SHA256 on uxmhf-rpi3

Feature to add SHA256 support to libxmhfcrypto for both hash and hmac. Based upon libtomcrypt.

PR created with updates. Modifies uhsign uapp to use SHA256 HMAC instead of SHA1 HMAC.

PR reviewed and merged:

Thanks @Cap. Moved to tasks category and updated OP with PR.

PR merged, updated OP. Closing task thread. Thanks @Cap!