pdl: Align Rust canonical tests with source

I’ve been copying bits and pieces from the source files into the Rust
file and the definition has been accidentally reordered. They’re now
brought back in line with the source files.

Test: atest pdl_tests pdl_rust_generator_tests_{le,be}
Change-Id: I41c26557b90e5f17e3dc7304def6f2dbb1e09ec3