Allow for 32-bit VTS builds

In 32-bit builds a `long` may be 32 bits, but the `long` values on an
AIDL interface are 64 bits.  Therefore need to use `int64_t` for the
corresponding C++ type, not `long`.

Bug: 271056044
Test: VtsAidlKeyMintTargetTest --gtest_filter="*AuthTest*" (32-b)
Change-Id: I19f5a1d825dfcc45087534bbd4239a13cdfec3f7