headers: put the [v1_enum] in bdatypes.h on one line

Otherwise it results in a compilation error with widl 6.0-rc1:
  include/bdatypes.h:43: error: 'PBDA_EVENT_ID': [v1_enum] attribute applied to non-enum type

The code generated without this [v1_enum] is the same but we can keep this
information.
1 file changed