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/T1023RDB_defconfig b/configs/T1023RDB_defconfig
index fddfe95..eb5d4ef 100644
--- a/configs/T1023RDB_defconfig
+++ b/configs/T1023RDB_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_T102XRDB=y
 CONFIG_SYS_EXTRA_OPTIONS="PPC_T1023,T1023RDB"
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y