mm: move hugepage test examples to tools/testing/selftests/vm

mm: move hugepage test examples to tools/testing/selftests/vm

hugepage-mmap.c, hugepage-shm.c and map_hugetlb.c in Documentation/vm are
simple pass/fail tests, It's better to promote them to
tools/testing/selftests.

Thanks suggestion of Andrew Morton about this.  They all need firstly
setting up proper nr_hugepages and hugepage-mmap need to mount hugetlbfs.
So I add a shell script run_vmtests to do such work which will call the
three test programs and check the return value of them.

Changes to original code including below:
a. add run_vmtests script
b. return error when read_bytes mismatch with writed bytes.
c. coding style fixes: do not use assignment in if condition

[[email protected]: build the targets before trying to execute them]
[[email protected]: Documentation/vm/ no longer has a Makefile. Fixes "make clean"]
Signed-off-by: Dave Young <[email protected]>
Cc: Wu Fengguang <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>