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/T1023RDB_SPIFLASH_defconfig b/configs/T1023RDB_SPIFLASH_defconfig
index 5f75bd6..b72fc86 100644
--- a/configs/T1023RDB_SPIFLASH_defconfig
+++ b/configs/T1023RDB_SPIFLASH_defconfig
@@ -6,6 +6,7 @@
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y