of: unittest: Add a test case for for_each_of_imap_item iterator

of: unittest: Add a test case for for_each_of_imap_item iterator

Recently for_each_of_imap_item iterator has been introduce to help
drivers in parsing the interrupt-map property.

Add a test case for this iterator.

Signed-off-by: Herve Codina (Schneider Electric) <herve.codina@bootlin.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patch.msgid.link/20260114093938.1089936-3-herve.codina@bootlin.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>