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/dra74_evm_defconfig b/configs/dra74_evm_defconfig
index d18d89a..7bff294 100644
--- a/configs/dra74_evm_defconfig
+++ b/configs/dra74_evm_defconfig
@@ -15,5 +15,6 @@
 CONFIG_DM=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_BAR=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_SYS_NS16550=y
 CONFIG_TI_QSPI=y