sf: Move SPI flash drivers to defconfig

There are already Kconfig options for SPI flash drivers, but we
have not moved them from config.h to defconfig files. This commit
does this in a batch.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/mx6qpsabreauto_defconfig b/configs/mx6qpsabreauto_defconfig
index 3e9506a..c44cd8f 100644
--- a/configs/mx6qpsabreauto_defconfig
+++ b/configs/mx6qpsabreauto_defconfig
@@ -4,3 +4,4 @@
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6qsabreauto/mx6qp.cfg,MX6Q"
 CONFIG_CMD_GPIO=y
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_STMICRO=y