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/alt_defconfig b/configs/alt_defconfig
index 479b4a5..aaf6a99 100644
--- a/configs/alt_defconfig
+++ b/configs/alt_defconfig
@@ -19,3 +19,4 @@
 CONFIG_SH_SDHI=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_BAR=y
+CONFIG_SPI_FLASH_SPANSION=y