Add a build target for bootloader tests

Since the .py files don't need to be built, they can be packaged
as-is. We can use a PHONY_PACKAGE with the source files set as
the target's LOCAL_PICKUP_FILES to make them accessible to
packaging targets like google_tests.

Test: make bootloader_unit_test
Bug: 33559158
Change-Id: I4a4453481d25a7dacb5bd8e8680328350d95f553
1 file changed