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/P4080DS_SDCARD_defconfig b/configs/P4080DS_SDCARD_defconfig
index 3fad614..4a0a65d 100644
--- a/configs/P4080DS_SDCARD_defconfig
+++ b/configs/P4080DS_SDCARD_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_P4080DS=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