Refactor IC support for RKP

Remote key provisioning means that attestation keys and certs are
passed in, and not pulled directly from the factory-provisioned data.

In anticipation of RKP support, parameterize/refactor some existing
functions so that we can pass keys to them. Also new extern functions
for generating an RKP-attested key as well as keypair/cert for testing.

Test: VtsHalIdentityTargetTest
Bug: 194696876
Change-Id: I7d2906de04835906682455952ebe238c3fa57321