selftests: prctl: Add new prctl test for PR_SET_VMA action

This patch will add the new test, which covers the prctl call with
PR_SET_VMA command. The test tries to give a name to the anonymous
VMA within the process memory map, and then checks the result of
the operation by parsing 'maps' virtual file.

Additionally, the test tries to call the prctl PR_SET_VMA command
with invalid arguments, and checks the error codes for correctness.

At the moment anonymous VMA naming through prctl call functionality
is not covered with any tests, so I think implementing it makes sense.

In version 2 of this patch I consider the selftest Makefile rule about
TARGETS entries order - I moved the 'prctl' entry in the Makefile to
follow the lexicographic order. In version 1 it was placed at the
end of the list.

Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>