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/P1020RDB-PC_SPIFLASH_defconfig b/configs/P1020RDB-PC_SPIFLASH_defconfig
index 3209aa7..3a26800 100644
--- a/configs/P1020RDB-PC_SPIFLASH_defconfig
+++ b/configs/P1020RDB-PC_SPIFLASH_defconfig
@@ -4,6 +4,7 @@
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="P1020RDB_PC,SPIFLASH"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y