Please enable SATA command option into U-Boot. Meanwhile, you can change configuraiton and store the boot command into SATA. Take MX6Q SabreSD board as the example, the following changes are needed.
diff --git a/include/configs/mx6q_sabresd.h b/include/configs/mx6q_sabresd.h
index 0cd57d9..68e7bec 100644
--- a/include/configs/mx6q_sabresd.h
+++ b/include/configs/mx6q_sabresd.h
@@ -103,7 +103,7 @@
#define CONFIG_CMD_CLOCK
#define CONFIG_REF_CLK_FREQ CONFIG_MX6_HCLK_FREQ
-/* #define CONFIG_CMD_SATA */
+#define CONFIG_CMD_SATA
#undef CONFIG_CMD_IMLS
#define CONFIG_CMD_IMX_DOWNLOAD_MODE
@@ -300,9 +300,9 @@
#define CONFIG_SYS_NO_FLASH
/* Monitor at beginning of flash */
-#define CONFIG_FSL_ENV_IN_MMC
+/* #define CONFIG_FSL_ENV_IN_MMC */
/* #define CONFIG_FSL_ENV_IN_NAND */
-/* #define CONFIG_FSL_ENV_IN_SATA */
+#define CONFIG_FSL_ENV_IN_SATA
#define CONFIG_ENV_SECT_SIZE (8 * 1024)
#define CONFIG_ENV_SIZE CONFIG_ENV_SECT_SIZE
Lily