selftests: vm: update .gitignore with new test

Update .gitignore with new test.

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

tools/testing/selftests/vm/.gitignore

@@ -11,3 +11,4 @@ mlock-intersect-test
 mlock-random-test
 virtual_address_range
 gup_benchmark
+va_128TBswitch