After I read relevant info online, I think (but not sure) that when uboot.env is used, the new am335x-evmsk.dtb is read for the device driver. A general kernel build can support variant devices through .dtb file.
The recent kernel still supports the old uEnv.txt file. As the online web page says that the old kernel has to rebuild for different devices/processors. My question here is that how the new kernel can support uEnv.txt?
Has the kernel included two parts for new .dtb and the the old device drivers?