on the iMX6Q there is a fuse from which you can read the temperature grade of the CPU. It can be found in the reference manual in chapter 5.2 ("Fusemap Description Table") and is located at fuse address 0x480[7:6].
For the iMX6SDL, there is no such fuse documented. I tried reading the same address, hoping that the information is there and just undocumented, but I had no luck. The according address reads 0 (= "consumer") on my device, but I know it is an "extended consumer" device.
Is there a way to find out the temperature grade of an iMX6SDL via software?