lib: add module support to crc32 tests

Extract the crc32 test code into its own source file, to allow to
compile it either to a loadable module, or builtin into the kernel.

Link: http://lkml.kernel.org/r/1483470276-10517-1-git-send-email-geert@linux-m68k.org


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>