selftests: vm: Build/Run 64bit tests only on 64bit arch

Some virtual address range tests requires 64bit address space,
and we can not build and run those tests on the 32bit machine.

Filter the 64bit architectures in Makefile and run_vmtests,
so that those tests are built/run only on 64bit archs.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>