Do you have a u-boot which supported UHS-I mode in i.MX6DQ?
We confirmed the Linux kernel was supported UHS-I mode in android L5.0.0_1.0.0.
(UHS-I [SDR104]: 1.8V signaling, Frequency up to 208 MHz, up to 104MB/sec)
But, u-boot wasn't supported it.
(i.e. High Speed mode: 3.3V signaling, Frequency up to 50 MHz, up to 25 MB/sec)