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/P5040DS_NAND_SECURE_BOOT_defconfig b/configs/P5040DS_NAND_SECURE_BOOT_defconfig
index 2b21d27..063e0f7 100644
--- a/configs/P5040DS_NAND_SECURE_BOOT_defconfig
+++ b/configs/P5040DS_NAND_SECURE_BOOT_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_P5040DS=y
 CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,NAND,SECURE_BOOT,SYS_TEXT_BASE=0xFFF40000"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y