iio: accel: bma400: Rename activity_event_en() to generic_event_en()

iio: accel: bma400: Rename activity_event_en() to generic_event_en()

The function activity_event_en() configures the generic interrupts
GEN1 and GEN2, which are used for activity and inactivity detection
as per the datasheet. The existing name is misleading, since the
device also provides activity change and activity recognition
interrupts. Activity change interrupt is not supported yet whereas
Activity recognition interrupt is configured in a different function.

Rename activity_event_en() to generic_event_en() to better reflect its
actual purpose.

No functional changes intended.

Signed-off-by: Akshay Jindal <akshayaj.lkd@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>