[Testing] Inclrease timer test timeout and update default test targets

The threading test is verifying that the timer fires, not that it fires
within a specific timeout, so increasing to 100 to keep it from failing
randomly. Also removing xenia-cpu-ppc-tests from list of default targets
as they take forever to run, they can still be run run using xb test
with --target xenia-cpu-ppc-tests explicitly.

xenia-build.py

@@ -1223,7 +1223,8 @@ class TestCommand(BaseBuildCommand):
         # The test executables that will be built and run.
         test_targets = args["target"] or [
             "xenia-base-tests",
-            "xenia-cpu-ppc-tests"
+            "xenia-cpu-tests",
+            "xenia-kernel-tests",
             ]
         args["target"] = test_targets