Add utility method to perform HMAC agreement

To make it easier for clients (vold & keystore) to perform key
agreement, this CL adds a service method that does it.  To make key
agreement consistent, this method sorts the HMAC sharing parameters
lexicographically.  The requirement for sorting is documented in the
HAL.

Test: Boot device
Bug: 79307225
Bug: 78766190
Change-Id: Idb224f27f8e4426281d9a0105605ba22bf7c7e95