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/bf525-ucr2_defconfig b/configs/bf525-ucr2_defconfig
index 6406f20..15a8f1f 100644
--- a/configs/bf525-ucr2_defconfig
+++ b/configs/bf525-ucr2_defconfig
@@ -6,3 +6,4 @@
 # CONFIG_CMD_NET is not set
 # CONFIG_CMD_NFS is not set
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_EON=y