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/P1025RDB_NAND_defconfig b/configs/P1025RDB_NAND_defconfig
index 58fb6a8..1c5e06a 100644
--- a/configs/P1025RDB_NAND_defconfig
+++ b/configs/P1025RDB_NAND_defconfig
@@ -5,6 +5,7 @@
 CONFIG_TPL=y
 CONFIG_SYS_EXTRA_OPTIONS="P1025RDB,NAND"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y