lib: add module support to linked list sorting tests

lib: add module support to linked list sorting tests

Extract the linked list sorting 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/[email protected]
Signed-off-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>