ANDROID: trusty-core: export trusty_fast_call64()

trusty_fast_call64() isn't used, so maybe it should just be removed.
But for any of the Trusty driver modules besides trusty-core to start
using it, it needs to be exported, analogous to trusty_fast_call32().

Change-Id: Id25aa4e8545753b2ccb8c7bb595d563bb7d8e9b3
Signed-off-by: Eric Biggers <ebiggers@google.com>