iio: imu: adis_buffer: split trigger handling

iio: imu: adis_buffer: split trigger handling

Split trigger handling for devices that have paging and need to
select the correct page to get the data. Although this actually
introduces more LOC, it makes the code and the locking clear. It will
also make the following move to the cleanup magic cleaner.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240618-dev-iio-adis-cleanup-v1-1-bd93ce7845c7@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>