iio: imu: adis16475.c: Add delta angle and delta velocity channels

Add support for delta angle and delta velocity raw and buffer
readings to adis16475 driver.
Signed-off-by: Ramona Bolboaca <ramona.bolboaca@analog.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20230808075059.645525-4-ramona.bolboaca@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>