of/irq: Export of_irq_count for modules

of/irq: Export of_irq_count for modules

Need to export `of_irq_count` in preparation for modularizing the Exynos
MCT driver which uses this API for setting up the timer IRQs.

Signed-off-by: Will McVicker <willmcvicker@google.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Youngmin Nam <youngmin.nam@samsung.com>
Reviewed-by: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250620181719.1399856-2-willmcvicker@google.com