lib/string_choices: Add str_assert_deassert() helper

lib/string_choices: Add str_assert_deassert() helper

Add str_assert_deassert() helper to return "assert" or "deassert"
string literal depending on the boolean argument. Also add the
inversed variant str_deassert_assert().

Suggested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20250923095229.2149740-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Kees Cook <kees@kernel.org>