iio: adis16480: make the burst_max_speed configurable

iio: adis16480: make the burst_max_speed configurable

With this, we can pass the maxixum spi burst speed to the
'ADIS16480_DATA()' macro. This is in preparation to support new devices
that have a different speed than the one used so far.

Co-developed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Ramona Gradinariu <ramona.gradinariu@analog.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240528142409.239187-2-ramona.gradinariu@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>