Fix test suite data files issue.

The current test suite rule implementation has a bug where test data
files are excluded from the final suite zip files when a suite doesn't
have a designated testcases output directory, which is represented by
COMPATIBILITY_TESTCASES_OUT_$(suite_name).

Specifically, the rule that collects test data files for each suite
filters out suite output paths that conflict with module output paths,
which happens when a suite doesn't have its own testcases output
directory. It seems to have been done this way just to avoid make rule
conflict errors, but it ended up causing missing test data files.

This change fixes it by adding an indexing purpose only test suit file
variable.

Fixes: 140761783
Test: m general-tests
Test: Compared before vs after, no meaningful differences.
Test: Changed bc-tests to a device test and built general-tests.
Test: Before - data files missing, after - data files present
Change-Id: I2008992f4144c6ee115f4b4e4ac9caa4312bbe34