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/aristainetos_defconfig b/configs/aristainetos_defconfig
index 5e9f220..15fc3a9 100644
--- a/configs/aristainetos_defconfig
+++ b/configs/aristainetos_defconfig
@@ -6,3 +6,4 @@
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_STMICRO=y