perf build: Rename TEST_LOGS to SHELL_TEST_LOGS

Rename TEST_LOGS to SHELL_TEST_LOGS as later changes will add more
kinds of test logs.
Minor comment tweak in Makefile.perf as more than just test shell
tests are checked.

Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250311213628.569562-3-irogers@google.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>