pdl: Simplify the generation of unit tests

Instead of copy-pasting the PDL code for little- and big-endian unit
tests, we can use a macro to handle this for us. This also helps
enforce a consistent naming scheme for the auto-generated files.

Test: atest pdl_tests
(cherry picked from https://android-review.googlesource.com/q/commit:745b08d7c7b68ad9976bc67200b59282bf78d43f)
Merged-In: I3d124501a22e807c42b498b10357d8cedf456244
Change-Id: I3d124501a22e807c42b498b10357d8cedf456244