kselftests: enable mremap tests in vts

Enable mremap_dontunmap and mremap_test because Android uses fast
mremap to optimize stop the world pause in userfaultfd ART GC. This has
interesting interactions with android out-of-tree speculative page
faults.

Test: atest vts_linux_kselftest_arm_64:vm_mremap_dontunmap_arm_64#vm_mremap_dontunmap_arm_64
Test: atest vts_linux_kselftest_arm_64:vm_mremap_test_arm_64#vm_mremap_test_arm_64
Bug: 264573101
Change-Id: Idf3d4f800326f8c673c90aa691f1f5badf87082a
Signed-off-by: Edward Liaw <edliaw@google.com>
4 files changed