[rkpd] Refactor rkpd_client into an independent lib for reuse

This allows rkpd_client to be reused by both keystore2 and
AVF pVM remote attestation.

Test: atest keystore2_test librkpd_client.test
Bug: 241428146
Change-Id: Ibdf95c4deb2ba499daaecd170c2971cda4e80bba
8 files changed