genirq/test: Depend on SPARSE_IRQ

Some architectures have a static interrupt layout, with a limited number of
interrupts. Without SPARSE_IRQ, the test may not be able to allocate any
fake interrupts, and the test will fail. (This occurs on ARCH=m68k, for
example.)

Additionally, managed-affinity is only supported with CONFIG_SPARSE_IRQ=y,
so irq_shutdown_depth_test() and irq_cpuhotplug_test() would fail without
it.

Add a 'SPARSE_IRQ' dependency to avoid these problems.

Many architectures 'select SPARSE_IRQ', so this is easy to miss.

Notably, this also excludes ARCH=um from running any of these tests, even
though some of them might work.

Fixes: 66067c3c ("genirq: Add kunit tests for depth counts")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/all/20250822190140.2154646-5-briannorris@chromium.org