selftest/futex: Reintroduce "Memory out of range" numa_mpol's subtest

Commit d8e2f919 ("selftests/futex: Fix some futex_numa_mpol
subtests") removed the "Memory out of range" subtest due to it being
dependent on the memory layout of the test process having an invalid
memory address just after the `*futex_ptr` allocated memory.

Reintroduce this test and make it deterministic, by allocation two
memory pages and marking the second one with PROT_NONE.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>