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/P3041DS_NAND_defconfig b/configs/P3041DS_NAND_defconfig
index 9b38983..d8fa407 100644
--- a/configs/P3041DS_NAND_defconfig
+++ b/configs/P3041DS_NAND_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_P3041DS=y
 CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,NAND,SYS_TEXT_BASE=0xFFF40000"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y