usercopy: Convert test_user_copy to KUnit test

Convert the runtime tests of hardened usercopy to standard KUnit tests.

Additionally disable usercopy_test_invalid() for systems with separate
address spaces (or no MMU) since it's not sensible to test for address
confusion there (e.g. m68k).

Co-developed-by: Vitor Massaru Iha <vitor@massaru.org>
Signed-off-by: Vitor Massaru Iha <vitor@massaru.org>
Link: https://lore.kernel.org/r/20200721174654.72132-1-vitor@massaru.org


Tested-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>