selftests: timers: Update .gitignore with newly added tests

Update .gitignore with newly added tests.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/timers/.gitignore

@@ -18,3 +18,5 @@ threadtest
 valid-adjtimex
 adjtick
 set-tz
+freq-step
+rtctest_setdate