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_SDCARD_defconfig b/configs/P1020RDB-PC_SDCARD_defconfig
index a6047f8..4ed2f7c 100644
--- a/configs/P1020RDB-PC_SDCARD_defconfig
+++ b/configs/P1020RDB-PC_SDCARD_defconfig
@@ -4,6 +4,7 @@
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="P1020RDB_PC,SDCARD"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y