refer to the Table 5-6. MMC/eMMC Boot Fusemap of imx6ul reference manual, BOOT_CFG2[5-7] can choose bus width:
Bus Width:
000 - 1-bit
001 - 4-bit
010 - 8-bit
101 - 4-bit
DDR (MMC 4.4)
110 - 8-bit
DDR (MMC 4.4)
Else - Reserved
then try the patch to support 8bit emmc
diff --git a/include/configs/mx6ul_14x14_evk.h b/include/configs/mx6ul_14x14_evk.h
index aabe2f7..b05b71f 100644
--- a/include/configs/mx6ul_14x14_evk.h
+++ b/include/configs/mx6ul_14x14_evk.h
@@ -426,4 +426,6 @@
#include "mx6ul_14x14_evk_android.h"
#endif
+#define CONFIG_MX6UL_EVK_EMMC_REWORK
+
#endif