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/dreamplug_defconfig b/configs/dreamplug_defconfig
index 0bb5f3a..966fa9e 100644
--- a/configs/dreamplug_defconfig
+++ b/configs/dreamplug_defconfig
@@ -10,4 +10,5 @@
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_PING=y
 CONFIG_SPI_FLASH=y
+CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_SYS_NS16550=y