futex_wait_thp: Add basic transparent hugepages test

Create a new functional test to allocate a transparent hugepage, then
futex_wait on a futex from each page in the hugepage. Perform a basic
wait with timeout simply to verify functionality.

Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Darren Hart <dvhart@infradead.org>