[Encrypted IMSI] Add support for EAP Method prefix

Add support for EAP method prefix in the anonymous identity
used during EAP-SIM/AKA/AKA' authentication when encrypted IMSI
is used. Added a new boolean field enable_eap_method_prefix_bool
in CarrierConfig, set to False as default.

Bug: 142915637
Test: atest TelephonyUtilTest
Change-Id: Ib184433aca550c19470354ab1c64295e3d9d3bce