I did some more research into the ads1015 driver. It seems you must setup a trigger prior to enabling the buffer. I suppose the device/driver only supports triggered buffers. To setup a trigger you can see the solution on this other thread: Colibri imx6ULL and Iris Carrier - ADC problems - #2 by daniel_m.tx
On my device once I setup a trigger I was able to enable the buffer via sysfs:
root@verdin-imx8mm-06827778:~# cat /sys/devices/platform/soc@0/soc@0\:bus@30800000/30a20000.i2c/i2c-0/0-0049/iio\:device0/buffer/enable
1
Best Regards,
Jeremias