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/P1022DS_36BIT_defconfig b/configs/P1022DS_36BIT_defconfig
index 78221fb..5646062 100644
--- a/configs/P1022DS_36BIT_defconfig
+++ b/configs/P1022DS_36BIT_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_P1022DS=y
 CONFIG_SYS_EXTRA_OPTIONS="36BIT"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y