Each entry in BCC is signed by its parent. BCC validator should be able to
validate the signature along the chain.
In OPK reference, EdDSA is used. Also adding functions to support ECDSA
in oemcrypto_ecc_key module.
Test: opk_ta_p40
Bug: 300310163
Bug: 307968622
Change-Id: Ibed895933eeb71b18c467604588cca449cac1af9