lib/cmdline_kunit: add test case for memparse()

lib/cmdline_kunit: add test case for memparse()

Better late than never, now there is a long-awaited basic test for
'memparse()' which is provided by cmdline.c.

Link: https://lore.kernel.org/20260519172259.908980-5-dmantipov@yandex.ru
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Charlie Jenkins <thecharlesjenkins@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>