iio: dac: ad5766: add missing select IIO_(TRIGGERED_)BUFFER in Kconfig

iio: dac: ad5766: add missing select IIO_(TRIGGERED_)BUFFER in Kconfig

This driver makes use of triggered buffers, but does not select the
required modules.

Add the missing 'select IIO_BUFFER' and 'select IIO_TRIGGERED_BUFFER'.

Fixes: 885b9790c25a ("drivers:iio:dac:ad5766.c: Add trigger buffer")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20241003-iio-select-v1-8-67c0385197cd@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>