Move tag type comments where they belong.

Because AIDL doesn't allow tag values to be constructed the way we
did in HIDL (and before), each tag definition carries a comment
specifying what the "magic" tag type value used in its construction
means.  This CL moves those comments so they're adjacent to the value
they're documenting.

Test: Build
Change-Id: I30b037f9ddf6bf2b07326a53959d490e045c891a