This allows Widevine RKP HAL to query BCC signature via DRM interface
during BCC extraction for remote provisioning phase 3. The query returns
the "additional_signature" field from
OEMCrypto_GetBootCertificateChain().
Test: Manual BCC extraction on Pixel 9
Bug: 355160637
Change-Id: I1a310a80c0cfef82ee3697f06c1293d5c1c3896a