imx: mx6ulevk: add CONFIG_SPI_FLASH_STMICRO

Add CONFIG_SPI_FLASH_STMICRO to let qspi driver can detect the
qspi chips.
"
=> sf probe
SF: Detected N25Q256 with page size 256 Bytes, erase size 64 KiB, total 32 MiB
"

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Jagan Teki <jteki@openedev.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>

include/configs/mx6ul_14x14_evk.h

@@ -203,6 +203,7 @@
 #define CONFIG_SF_DEFAULT_CS		0
 #define CONFIG_SF_DEFAULT_SPEED	40000000
 #define CONFIG_SF_DEFAULT_MODE		SPI_MODE_0
+#define CONFIG_SPI_FLASH_STMICRO
 #define FSL_QSPI_FLASH_NUM		1
 #define FSL_QSPI_FLASH_SIZE		SZ_32M
 #endif