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_SDCARD_defconfig b/configs/P5040DS_SDCARD_defconfig
index 1150d1d..d78bea0 100644
--- a/configs/P5040DS_SDCARD_defconfig
+++ b/configs/P5040DS_SDCARD_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_P5040DS=y
 CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,SDCARD,SYS_TEXT_BASE=0xFFF40000"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y