Staging: iio: Make IIO depend on GENERIC_HARDIRQS

On m68k (which doesn't support generic hardirqs yet):

drivers/staging/iio/industrialio-trigger.c: In function ‘iio_trigger_poll’:
drivers/staging/iio/industrialio-trigger.c:180: error: implicit declaration of function ‘generic_handle_irq’
drivers/staging/iio/industrialio-trigger.c: In function ‘iio_trigger_poll_chained’:
drivers/staging/iio/industrialio-trigger.c:200: error: implicit declaration of function ‘handle_nested_irq’
drivers/staging/iio/industrialio-trigger.c: In function ‘iio_trig_release’:
drivers/staging/iio/industrialio-trigger.c:379: error: implicit declaration of function ‘irq_modify_status’
drivers/staging/iio/industrialio-trigger.c:382: error: implicit declaration of function ‘irq_set_chip’
drivers/staging/iio/industrialio-trigger.c:384: error: implicit declaration of function ‘irq_set_handler’
drivers/staging/iio/industrialio-trigger.c:388: error: implicit declaration of function ‘irq_free_descs’
drivers/staging/iio/industrialio-trigger.c: In function ‘iio_trig_subirqmask’:
drivers/staging/iio/industrialio-trigger.c:402: error: implicit declaration of function ‘irq_data_get_irq_chip’
drivers/staging/iio/industrialio-trigger.c:402: warning: initialization makes pointer from integer without a cast
drivers/staging/iio/industrialio-trigger.c: In function ‘iio_trig_subirqunmask’:
drivers/staging/iio/industrialio-trigger.c:411: warning: initialization makes pointer from integer without a cast
drivers/staging/iio/industrialio-trigger.c: In function ‘iio_allocate_trigger’:
drivers/staging/iio/industrialio-trigger.c:432: error: implicit declaration of function ‘irq_alloc_descs’
drivers/staging/iio/industrialio-trigger.c:455: error: ‘handle_simple_irq’ undeclared (first use in this function)
drivers/staging/iio/industrialio-trigger.c:455: error: (Each undeclared identifier is reported only once
drivers/staging/iio/industrialio-trigger.c:455: error: for each function it appears in.)

Hence IIO_TRIGGER should depend on GENERIC_HARDIRQS.
But as IIO_TRIGGER and IIO_RING_BUFFER form a maze of dependencies and selects,
just make the whole IIO subsystem depend on GENERIC_HARDIRQS.

This dependency also covers !S390, so that one can be removed again.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>