iio: backend: add a modified prbs23 support

Support ADI specific prb23 sequence that can be used both for
calibrating or debugging digital interfaces.
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240802-dev-iio-backend-add-debugfs-v2-3-4cb62852f0d0@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

include/linux/iio/backend.h

@@ -56,6 +56,8 @@ enum iio_backend_test_pattern {
 	IIO_BACKEND_NO_TEST_PATTERN,
 	/* modified prbs9 */
 	IIO_BACKEND_ADI_PRBS_9A = 32,
+	/* modified prbs23 */
+	IIO_BACKEND_ADI_PRBS_23A,
 	IIO_BACKEND_TEST_PATTERN_MAX
 };